Have had it happen multiple times. Sometimes friends ask and sometimes its a sneak attack. Sometimes I get the "its for good luck" thing. Their reaction to the feel varies haha. I think it's always a friendly gesture and I definitely appreciate the positive feedback.
Idk if you guys ever do this, but sometimes, if i can tell their eyeing it, i'll just ask 'em if they wanna rub it. It's usually funny. Works great on the waitress if she's being flirty.