Like, okay, maybe it's because I've been asked to go somewhere with a dude exactly once (and only because my friends made him), but I can honestly see no reason for rejecting a guy unless you're in a relationship or like really, really don't want one.
But like... if you don't want a relationship then you don't want one. So I don't get if you say no to one person and yes to another, that doesn't make any sense to me.
And if you say you'd say yes to someone, and then they ask you, and you say no... then I really don't understand where you're coming from....
PSA: Guys have feelings too.