Social tip: If you run into an acquaintance and you forgot their name, don't make it awkward, just ask again.

I've run into this myself at college when I've met a few loose acquaintances I knew from high school. I call them by their name and say hello and it's obvious they forgot my name.

Dude, just ask again. I don't care. In fact, it would make me feel better to know you're at least making an attempt. So if you run into somebody and forget their name, don't worry about it, just ask again. They probably don't care either.