It's not Martyn H, as he clearly looks to have just caught wind of it. It must have been Tom as he's nearby & is laughing at dropping such a bomb from such a little guy. Slayed has also caught wind of it & thus his reaction. Ian looks to have inhaled & Mushy is trying to flee the rancid odor. Luckily Ian has slipped a gas mask/cap over whoever it is next to the culprit, to keep him from passing out. (Sorry I don't recognize who is in front of Ian.)
Ciall & Joey appear to be the only ones in the back rows to have already caught wind of the offense. Big John should have, but he's likely immune to such a stench.
![Stick Out Tongue :p :p](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)