I would have let him know that he is rude and uncouth, hopefully you won't be going to the lake with him again anytime too soon.
What do you do if you went to the lake with a guy you like, and he told you "you have a camel toe"? I can't get it off my mind.
From The Princess Bride, which has many great quotes:
Vizzini: He didn’t fall?! Inconceivable!
Inigo Montoya: You keep using that word. I do not think it means what you think it means.