I've known some of "these people". Couple of pointers.

First, resist the urge to hold you breath too much. Sounds counter productive, but this is not a situation where you want to lower the amount of oxygen reaching your brain. But also, the more you breathe it in, the sooner you start to become nose blind to the worst elements of the aroma.

Second, try not to laugh when you inevitably have to ask "where should I move this stuff in the seat?" even though you already know the answer is going to be "just throw it on the floor".