how rough is to rough?

okay. me and my partner for super ... kinky? last night I guess you could say. he likes being controlled and in control sometimes. it's kinda a bac a forth thing. but he does this thing were I like command him .. I don't know go down on me.. and he says yes ma'am. I'm fine with that but he forgot to say ma'am once and o jus blew it off and kept going later that night he said he wants me to punish him by slapping him if he does that.😳 honestly Im not sure I could hit him. it's really something he wants but I think it may be to rough.