hm. the others said it rather well, but in general, if i'm talking to you at all, then usually it's either because i'm bored, but otherwise in a good mood, and you're a handy ear and mouth, OR it's because i actually like (or think i could like) your company.
i don't much care for heavily engaging others that i know i'll bump in to regularly unless i'm pretty sure that i won't mind talking to them when i do. it's too easy to accidentally lead others into thinking that i want to be BFFs, so i'm careful who i encourage (don't want to have to hurt anyone's feelings by having to avoid them thus confusing them when really they've done nothing wrong).
that said, basically, i'll try to make you laugh, if you have a problem and want help, i'll talk and listen (troubleshoot and tweak) as long as you want, until you're happy that you've at least found a tentative solution, things like that.
"friendly" things.