I have a 20 year old son. It has been my experience that young men have a very high tolerance for foul odors.
Your post made me smile

Still, I can't stop thinking about that BIG A$$ vent over the door to TA's master suite. The shower door was not floor to ceiling, and there's a massive vent over the door. I just can't imagine. The upstairs must have been on a single A/C unit, so the air had to be circulating. ugh
But yeah, I think they were just oblivious.