To pass gas that is extremely odiferous, super-loud/drawn-out, and/or copiously voluminous, so that said whizzpopper is noticeably more offensive than simply "cutting the cheese".
I chowed down on three bowls of fragrant steaming baked beans at the neighbors' backyard barbeque last evening, and now my butt-hole is parched and raw from having to slice the Limburger all night.
A slice on the mat is a Second War British term. It signifies the eager anticipation of a servicemanreturning home on leave; as his woman opens the door they can't even wait to get to the bedroom, and have sex there and then, on the mat, just inside the door. It is still used.
I hadn't seen her for three months, and when I turned up she immediately gave me a slice on the mat. She did remember to close the door, though. . .