“Scribble me a line” does that sound rude?

I’ve been using this construction for quite a long time, while giving anybody my contacts in the informal situations, meaning “write me if you have time and inspiration” and I have no idea where I caught it. Recently I’ve been talking to a person from USA and used the phrase, and I was told it sounds very peculiar. He never heard it and found it really strange and funny 🙂 So obviously I googled it and found out that the proper idiom is “drop somebody a line”. English isn’t my native language. My mistake, though word “scribble” does have the meaning “to write, not putting much effort in it”. But what shade of “not putting effort” does it have? I now, feel like I’ve been rude to people by using it, cause the word “scribble” may have some negative connotations? Like associate with clumsy and untidy? I shall not use it anymore but I’d like to know how grievous the mistake was 🙂 So my questions are to native speakers: have you ever heard this construction, can it exist and what feeling does this phrase give you? Thank you in advance!