I may actually have been on the other end of this situation!
I had a real "ground, please swallow me" moment in my late teens. It was past midnight, I'd had a couple of drinks, and I'd ended up sat next to this absolutely gorgeous girl.
I was doing really well - keeping it casual - when something made me blurt out, "This is going to sound weird, but you have amazing legs."
She didn't bat an eyelid. She just said "Thanks" in a fairly neutral tone, then sat waiting to see what I'd say next.
I chickened out and changed the subject.
Hitting on guys is so much less stressful than hitting on girls because I know the odds are in my favour. And even if I do end up making moves on a gay guy, they tend to be really understanding. (It's only happened to me once, and he was almost apologetic!)