I'm slightly retarded in that I picture me starting a conversation with someone else to be forcing myself on them. If you talk to me I'm glad to listen. If you listen back, I'll be glad to talk. If I'm glad to talk, I will keep on keepin' on till I think you're starting to get disinterested.
Honestly, it doesn't matter what it's about, so long as it touches on a subject of fascination (most subjects), isn't just small-talk, and seems sincere. I quickly become interested in things other people are, so long as they are genuine.