My boyfriend won't let go of what I said- help?

So I was on the phone with my bf and we were looking forward to seeing each other since we are long-distance right now. He suggested I wear something I'll say..specific.. to go see him and I called him disgusting but I didn't really mean it. He got VERY offended by it and has been upset at me for a while now but I didn't mean that he was.. I just thought the fact that he asked me to wear something kinda naughty made me feel gross so I called him disgusting but then he just got super offended and he will not accept my apology no matter how many times i try to tell him i didnt mean it... is this something u dont tell guys ever? He says I have to PROVE that hes not... im like, how do you do that? hes like idk you have to figure it out and i have no idea what to do.. please help, i want to resolve things b4 we see each other so we can have a good time. i know this might seem silly but I do want genuine help. thank you.