Snort!

Often when trying to stifle a cough, or avoid choking, I make sudden snorting noises that sound like I am stifling a laugh. It's annoying when someone who's not saying anything remotely worth mockery thinks I am snorting with derision, and responds to my 'laughter.'

person: "After she was tortured..."
brainhell: "Snort!"
person: "Heh heh! Yeah, I know."

Even worse is when they think I think they are Robin Williams, and keep making more jokes.

Far worse is when they know I don't think they are funny, but they think they are Robin Williams, and keep making more jokes.