What is the meaning of the phrase "we-find-each-other's-lame-jokes-funny vibe"?

People who know each other well - especially close friends - often share "in jokes." These are sayings, or references to past events, which are funny to those "in the know," but obscure, unfunny, or even offensive to those unfamiliar with the reference. The "vibe" is the sense or attitude that the two share or project.

For example, someone very knowledgeable about a topic may give off a vibe of confidence (or, less attractively, of arrogance).

In this case, Raghav and Aarti share a sense of humor (or perhaps the history described above), and that shared "vibe" is offensive to the writer.

You may think of it as the uncomfortable feeling you get when, at a party, you walk up to two friends who are speaking, and they stop talking and just look at you - you know you're on the outside, not part of the group.

The long, hyphenated expression describes a behavior shared by the characters Raghav and Aarti. It means that Raghav and Aarti both tell bad jokes, and Raghav and Aarti get enjoyment out of those bad jokes. They probably think, "Our jokes are terrible, but they're awesome because they're terrible. We don't care what you think."

I would infer from this that no one else finds Raghav and Aarti's jokes funny, and that the narrator thinks that they are pretentious.

The hyphenated construction draws attention to the artificiality of Raghav and Arti's "vibe" to make clear that the narrator is aware that it is a big charade.

My wife and I have a large number of "in-jokes" and sayings that other people either don't understand or do understand but don't find funny. And, of course, they aren't funny to anyone else...they are less jokes than they are relationship/friendship glue. This is the "vibe" that is being referred to but, in this context, the author is clearly put off by it.