How can I be left alone during the work day without looking awkward or offensive?

All of these are social situations, so people are expected to socialize. If I saw a colleague in a coffee shop alone, I would at least make eye contact and acknowledge their presence.

Lunch is the primary time and place when people network with coworkers. You can do and say things that aren't work at lunch, getting to know each other.

The bus is less social. Odds are that socialization on a bus is more a matter of convenience; as a person who avoids a social context is sometimes worried they're rude or offending the person they don't talk to. Coffee shops are excuses to get coffee, sure; but, they are purpose built to allow customers to mingle. If you just wanted coffee, there's a drive through (or your coffee maker at home).

Libraries are places to go to get that isolated time, they're built very differently, and the rules and expectations are tuned for exactly what you want. Most libraries also come with ample places to study.

If you want to hang out in social places, with the intent of not socializing, then the best answer is "don't do that"; but, for those places were most people don't go to talk, you can say. "Hey it's nice to see you; but, my bus time is where is wind down, so I'm sorry if I'm not a chatter box." And then don't talk.

A possible approach is the sandwich technique.

https://www.brighthubpm.com/resource-management/56534-the-sandwich-technique-for-giving-feedback/

Here's one way to adapt it.

1. Hey John! Good to see you!
2. I hope you don't mind if I don't talk much today, I've got this work to finish.
3. Oh, no need to leave, it's good to have company, I just can't talk right now.

Most people who aren't completely insensitive will say something like, "No worries, I'll let you get on with it" and probably make their excuses and leave. If they stay they will probably start to feel uncomfortable after not conversing for a while and they will say, "Good to see you, I have to get going". You can smile and say, "Sorry I couldn't talk today - hope you understand."

The added advantage is that next time they see you they probably won't assume they can sit down. If you spot them first just give a friendly wave, optionally mouth "Working!" with a smile, and immediately get your head down over your laptop.

If you want to chat, you can wave them over.

Note: If you are physically very attractive, this may make them want to be near you. Being good-looking has its advantages and disadvantages.

You've got a couple things going on; I'll try to separate them.

First of all is your desire to be left alone. Second is your desire to not be rude or to offend people.

I'll start with the non-offensive part first. Part of the challenge here is: what do you normally portray yourself as? Are you always trying to be left alone? Do you only want to interact with people on your terms? That's going to determine how the people that know you interpret your actions. I'm going to assume that you do not always want to be left alone and that you understand that interacting with people only on your terms will lead to you being always left alone.

Something that I've seen people do is this: when a colleague approaches, greet them warmly. Converse with them for a minute or two. This will establish that you are friendly and willing to talk. "Hey there! How are you? Are you still working on [X] project?" Something like that is a good way to start the interaction.

Then, after an exchange or two, I see the person say something like, "As much as I enjoy chatting, I've set this time aside to work/meditate/think/run through something in my mind. If you don't mind, I'd like to get back to that in the time I have left. It's good seeing you; let's chat at [x time]." That establishes boundaries yet says you are interested in interacting - just not right now. In your case, a response of "I'm working through my break; I've got a deadline and need to focus right now." may also be appropriate.

I've also seen people start the interaction off with something like, "Hey there; I'm in the middle of meditating on something; is there something I can do for you?". That's a little more direct and I wouldn't recommend having that be the first thing to say unless it's with someone who's exceptionally unwilling to grasp a clue.

I don't recommend acting bored with a conversation. That's just a poor interpersonal skill and establishes your reputation as someone unpleasant (or worse).

Additionally... people as a whole don't like pauses in conversation and try to fill it with something. For the above method to work, you'll need to be able to accept pauses in conversation and not need to fill them.

Despite your efforts at politeness, some people have very thin skins and will be offended at the drop of a hat. They've gotten used to getting what they want from this behavior; the challenge here is to not let that behavior manipulate you. Don't argue, don't get defensive. If someone does get offended at your being polite yet establishing boundaries, that's their problem and not yours. Be polite yet firm and when the other party sees that their behavior is unproductive, they'll eventually stop it.

I realize this answer may cover things you didn't ask about - but bear with me - they may be connected.

I read your question as a request for having some quiet time on your own, without being unnessecarily rude. There is nothing wrong with that at all, but it makes me wonder if you've given a thought to how you want your relationship with your co-workers to play out in the long run, besides the specific lunch situations.

The reason i ask is because the way you act will probably have a bearing on how people perceive you in a greater perspective. In other words, if wish to maintain at least a minimum of collegial friendship - generally speaking - you may have to put up with the occasional small talk during lunch in order to maintain the relationship.

On the other hand, if the relationship to your co-workers aren't that important to you, you are in your full right to make your own quiet time a priority. However there is a risk that this comes across as arrogant, or hurtful to some of the others even though you don't have any evil intentions at all.

Bottom line is that you may have to shift your priorities from time to time in order to maintain a minimum of functioning relationship to your surroundings on one hand, and to have the piece of mind you need on the other hand. Added to that, people may respect your wish for quiet time more if you've established a friendly relationship first.

Another way to approach this is to try to establish a new lunch time norm. This is heavily dependent on organizational culture, but there may be other coworkers wishing more lunch time alone besides you. Social pressure may make others small talk more than they'd like themselves, just to conform to a perceived norm. Sometimes a helpful reminder conveyed through our boss can clarify that some co-workers may need the occasional time alone, reminding others to be mindful and ask before barging in.

If you feel comfortable with it, you could politely convey your needs by letting others know that you don't want to be rude, but just need the time to recuperate during lunch. I realize this can be hard, but it can save others from guessing what they did wrong if you make your message verbose rather than trying to communicate your needs nonverbally.

Even if they ask I don't feel like saying don't sit with me due to it is usually considered rude. They asking either what's wrong or got offended.

When I can feel that the other person who sat on the chair next to me is kinda stuck in a conversation, and just carrying it on, I tell them up front not to feel bad about leaving the conversation. I tell them that they're not pressured to continue and I'm totally okay with not talking any longer at that moment either. This way they're welcome whenever they want and also leave on their own terms. So they have that control, and so do you.

The benefit is that they now know that I'm not very talkative. So they don't beat around the bushes and force a conversation. Similarly, I can also, at times, end the chat and say goodbye. It's a win for both parties where one doesn't feel that the other was rude since it has now become the norm.

I don't want to show extra effort such as like I am bored but what's the easiest way to do it?

Mostly, this question comes up "What are you doing?". Answer it a bit like you want to get back to the activity you were doing.

• I have this deadline and there's a significant amount of work left. Just wrapping that up. How about you?
• Reading this book with this (fav music or coffee).

People don't usually disturb you when you're reading something. If they see a YouTube video on your screen, sure they're going to recommend a video too!

Also, initiate a conversation yourself too! Don't always be the responder.