Comment and I will....

a) Tell you why I friended you.

b) Associate you with something -- a fandom, song, colour, photo, etc.

c) Tell you something I like about you.

d) Tell you a memory I have of you.

e) Ask you something I've wanted to know about you

f) Tell you my favorite userpic from your list

g) In return, you need to post this on your own LJ