The worst smelling ones are usually the quietest. Silent but violent.
I remember farting on my brother's face while he slept, right into that fucking snoring gob of his. Really loud and wet sounding, I tried to stop out of fear of shitting myself but I went well beyond the point of no return. The smell was woeful, smelling of rotten eggs mixed with spice. He woke up immediately after I farted and almost choked on the fumes.