Is it normal to rub up against a co-worker accidently a lot?

Hi everybody, this is my first question on here so sorry if i make any common mistakes. So i work as a massage therapist at a spa, its small and me and this other guy are literally the only 2 therapists there. because its small, we accidentally bump into each other.......a lot. My butt is almost always rubbing up against his crotch when we're setting up for our next clients. He's really nice and easy going and just laughs and makes a joke sometimes about it, but i know that he gets erections from me and that it cant be comfortable for him. It's my firm belief that it should never get sexual in the workplace, especially in my field. What do you all think i should do?