To do
something really badly. "To stink" means to do badly, "
joint" here means a place. "Stink up the
joint" is an exaggerated form meaning you "stink" so badly the whole place starts to stink, as if you've taken a shit.
"Oh no, Magnus! He blundered and lost his
Queen! Okay, now I don't feel
bad about my awful last game! Magnus is also stinking up the
joint just like me today!" -- Hikaru Nakamura, on a stream in an online chess tournament, 13.11.2025