wow never heard of such a thing in a gym. i would find a different gym, the environment of a gym is crucial to your success. its the Y and they aren't gonna do anything to him, a different gym would of banned him on the spot for that type of activity.. i know mine would of. the problem is the Y's management are a bunch of skinny dorks who have no clue what a gym should be. its the Y for goodness sake bro! whenever i have visited the Y where i used to live it was a bunch of retards (literally there was one creepy dude there that would stare at my gf when she would be at the pool the whole time, i found out that he was retarded from a car accident years ago otherwise i would have confronted him too), old people, and not a single person there was what i consider a real lifter. this dude you are dealing with obviously has mental issues and i would get the hell out of there.
also as far as your son leave him at home, you are going to the gym to workout period. i realize you probably like the Y cause they cater to families but if you want to be serious as a lifter you better find a real gym
the dude who runs my gym is a fucking horse, his biceps are the size of my head and he is there EVERYDAY either lifting himself or in his office stuffing his face.. THATS THE WAY a real manager should be. if some jerk acted like that he would of ran him out of there in 5 seconds ..