"You're cool but you're a tad bit too hoish/manhoish for me"
Sounds like they've had a 'crush' on a lot of people. Don't become a number!
you don't need to - you just decline their attention - if you want them to know why, that's your ego talking, and they'll feel it and it won't probably be a conversation that will go well
well, you might have some challenges then - good or bad, i can't say