Similar to the water:piss ratio regarding (US?) swimming pools, insofar as the knowledge that the "nostalgic" smell of swimming pools is not the comforting presence of chlorine so many believe it to be, and is in fact the confirmation of a volume of piss in the water that is rapidly nearing the extent of said chlorine's capacity to neutralize (sapped also by ceaseless sunshine & innumerable contaminants hitching rides on patrons' oblivious meatsacs).
In short: if you smell "pool", someone(s) have pissed in it. A lot.
Agreed, I take showers in the morning but sometimes I’ll end the night with a really hot bath, it helps my body not hurt in the morning if I’ve been working hard that day. I will take a piss before I get in the tub but I’ll be damned if I don’t almost always pee some while I’m laying in the tub relaxing. It’s never seemed to be anything to give a shit about to me but some people do seem hyper sensitive to that kind of thing. My partner and I have peed while in the bathtub together before and it didn’t gross either of us out. Maybe it would be more gross if our urine was dark yellow or more noticeable beyond feeling the warmth for less than a minute.
Nope, too much piss. Also, "peed while in the bathtub together" is a bit too far, and that's not even including possible eye contact. To illustrate: what simple thing makes eating a banana in public creepy/hot? Eye contact. You do you, but stay outta my tub.