He probably means he should focus on his acting career rather than spend time volunteering for deaf people or something ? ( I think he assumed that if MC is able to sign = to use sign language, it's because he works at the service of deaf people. I am unsure that he realized that our two love birds are romantically involved, i think he was imagining MC is a social worker / street educator or something like that.)
He was trying to offend him and the deaf guy by saying that. Like imagine your partner/friend e.g. needs to use wheelchair and you hang out with them, so you naturally helping them by pushing the chair. So let's just say that while hanging out you meet a person that is really mad at you so mad they can't just ignore you they need to annoy you. Anyways they notice that you're with person that is disable so they use that to make fun of you and of this person saying that your social worker just helping them, by saying that they're belittling the relationship you have with that person. It's a bit like saying that somebody parents are paying you to hang out with them
What does the context he mean by social work when he said that sentence?? Sorry I can't sometimes grasp some words