Let them be guys. Don't expect them to behave themselves around you. They might want to act in an uncivilized way. As long as they respect you and don't try anything funny regarding you, let them be guys. Let them grunt, groan, make weird noises and be disgusting.
If it was a family outing, then it would be treated differently. Since it's a trip with the guys, be prepared for weird. Just don't let them treat YOU disrespectfully.