Most Helpful Girl
I'd be flattered. That being said, I've been told I'm terrible at taking compliments, so it would probably come off as me being super awkward.
Assuming he's a stranger, I would have no right to call him 'ugly'. And a guy's attractiveness doesn't affect or determine whether or not something he does is nice. At least not in my opinion.
Plus, most good looking guys have their heads too far up their own butts to say anything complimentary to another anyway (no offence).