i generally realize that someone had been flirting with me several weeks after the fact, when they are already having sex with someone who can take a hint.
One time a waitress at my work almost fucked me in the back room from flirting.. I pinch a lot of asses too Also I stare at their ass until there is an opportunity to say something about it..
I followed a girl around campus today. She wasn't even at the same campus as me, but I stayed on the train with her to see where she went. I skipped my lecture to do it, it was worth it though, you don't see many women that look like her.
I've always been really flirtatious, so generally speaking I flirt back, assuming I didn't instigate it. These days I'm taking it easy. I've stopped it the last few times I've seen the flirting going somewhere.