Young kids. Their faces, actually, whether it's in person or in photos. I see them and I wonder if they're okay. I wonder if they are living through the same nightmares I had to endure growing up, and I look at their parents, wondering if they're secretly monsters when no one else is looking, or if they're stupid enough to leave them alone with a monster. So, walking through WalMart is like strolling through Hell for me.
Another trigger is my hair...if anyone other than my sisters or the VERY limited female friends that I have touches it, I snap. I can't stop myself from it, either; it's an automatic response. I have screamed at my son in public, humiliating the both of us, because he thought it would be funny to pull my hair while he walked behind me. (My bio-father had practically scalped me when I was younger; he picked me up by my hair and threw me into a wall). I don't remember any of that (or him), but my scalp remembers it, so I trust very few people with my hair, and they are all female.

I didn't know about what he'd done to my head/hair until about 10 years ago or so, almost 2 decades after the fact.