The piss thing happening once or twice in the entire manga, okay, I get it. Women have a shorter urethra and a more wider open outflow. It is actually pretty realistic for someone who's switched sex to not be prepared for this. But in-universe hasn't Mahiro been a girl for like, a year and a half at least? You'd think that'd be plenty of time to master the new plumbing.
I can sort of excuse Nekotofu for this, but Namori? This 100% has to be her having fun at Nekotofu's expense.