what's the point if he doesn't hear you fart and realize that you have so little disregard and respect for his company that you just sit around farting with him near by?
Kind of seems like the waste of a perfectly good fart to me. Unless it really stunk. Now, if that's the case it's funny because there would be that little moment where the element of surprise and stink would be overwhelming and you could crack a smile because you know that he knows you know he ate your air biscuit.