I shouldn't be too judgemental as nobody likes to be rejected, it can really sting. I'm just thinking of examples where people became quite rude or abusive.
A few years ago I turned down a guy who I thought was 'out of my league ' as he was a model. I had known him from school, we bumped into each other again years later.
I was interested but he wasn't, then soon after I ended up meeting someone else. The first guy unexpectedly got in touch to ask me out.
I said I'd be happy to go as friends if that was ok, he called me a freak and immediately blocked me.
I've had another friend where the man clearly wasn't used to being turned down, and he pretty much said to her, how on earth can you turn me down?