Yeah maybe it's like you guys said, but if you ask me, it's still an overreaction, isn't it? I agree that he could've used better words, but of course Aki didn't mean anything bad after all, he just wanted to let him know to leave his nipples alone for a while...
Knowing Aki, we all know that it's just the way he expresses himself (kinda rude/sharp)... Anyway, I guess we'll understand everything in the next chapter...

I'm 100% sure there must be something else going on. Given his attitude, it can't be just about him not being allowed to touch the nipples of course... If you notice, the exact point where Tomoharu gets mad is right when Aki says "you can still f*ck me down there", and he replies "I can't believe you just said that"... That's where you can see the switch. In the part right before, where Aki forbade him from touching his nipples for a month and Tomoharu simply thought they wouldn't do it at all, he just seems very surprised but not exactly angry...
Now I can't really think of an explanation but it's clear that this statement of Aki's upset him a lot for some reason...