This sort of conversation is both really easy and really difficult for me to write. Like many things, it's easy once one finds the starting point, but it's finding the starting point that can be difficult.
In the case of this conversation, I found inspiration in the simple fact that I wanted them sitting next to each other in spite of the fact that one might consider it a little weird. I got my conversation starter and the opportunity to lampshade that all at once!
Incidentally, lampshading basically just means pointing out something people are going to find odd anyway and saying "yeah, that's weird, you wanna fight about it?" It's a risky style of writing that often results in fisticuffs.