Ap,
I have to ask if you know this guy really? How is he to people in your gym? Are you very well respected in your gym? I ask because he my know you are a looked up to type of guy at his gym. He may very well feel bad if you tell him what you know about the situation with your mom.

The last thing in my mind would be how big of a fight this might turn into. Going at it with that in mind might just set the wrong tone. Telling him he can do this or that seems rather bold if you ask me. He might say sorry dude. Then you can say dont tell me tell her next time in. Shake his hand and be done.

My older guy sugestion is you might talk to him in private and let him now how offended your mom was when he was in the bank the other day. Maybe just a reminder that women in this world are mothers and sisters and wives to someone. No need to be an ahole back to him. Just maybe some simple shame on him type of shit.

Leave the agression with the weights. Not how you approach this cat. If I had to guess your mom had dealt with far more BS from customers then this piss comment.

Good luck. Just remain calm at all times. Freedom is sweet.