I made a comment about this last week saying I'm 100% sure it's not just about him not being allowed to touch the nipples... Ueda got really mad about a particular statement of Aki's, which is: "you can still f*ck me down there". It's from this moment that you can clearly see the change in Ueda. When they were talking at the police station he tells others: "what he said, I can't just forgive that". He was referring to that.
Some people said that it made him angry because it's like Aki was treating him like a s3x toy, like "yeah, you can just throw it down there"... Honestly I think it's still a crazy overreaction because it was clear what Aki meant! They've been together for a long time and he should know that he loves him, it's just his way of talking (a bit sharp/rude)...
Silly as it may seen can't agree with ueda this time aki has the right to deny nipple access it's his body