When I'm with a girl out in public, I've had male strangers say very disrespectful things like "Hell yeah, you two are getting laid tonight!" Or, "What the hell is a hot chick like you doing with a guy like him!" "C'mon back here honey, leave that guy!"
Most Helpful Girl
Ignore it. If she's with you its for a reason.1
Most Helpful Guy
Just pull her close to you and keep moving. Make her feel safe. If you confront the guys you're putting yourself in their same level, a low level. If you keep walking you demonstrate you're a grown man who knows how to not get involved with stupid immature behavior.
If the guy tries to touch her then that's a different story, in that case you do have to confront him.3