This is a trap. It feels dangerous; a setup for something. His drunken brain can't precisely identify what but ..

He reaches up and pulls the mask off completely. Over his head so he can hold it in one hand in case Len's plan was to fucking snatch it and leave him there to suffocate.

Having a life support system fully exposed on his back makes him incredibly vulnerable. It's an egotistical show of strength that something that could easily kill him is within easy reach of everyone he fights. Even having it under the jacket would give him more protection. But no, he's the type of person that won't back down from a fight, admit a weakness or ever ask for help.

Now here he is, holding his mask and fully aware of the limited amount of time he can do that before things will start to get real uncomfortable.

But he does want to know what Len is mad about. Actually cares about what he thinks, which is another thing he's going to shove away to never think about again. There's nothing for him to say other than more questions he's not getting the answers so he simply stands there looking drunkenly confused.