HAHA! I thought the same thing and asked why a few years ago. It turns out that Parm and Vomit (and a few other things) have a common ingredient responsible for the foul odor: butyric acid.
Snip form the wikipedia entry:
Butyric acid, (from Greek βουτυρος = butter) IUPAC name n-Butanoic acid, or normal butyric acid, is a carboxylic acid with structural formula CH3CH2CH2-COOH. It is notably found in rancid butter, parmesan cheese, and vomit, and has an unpleasant odor and acrid taste, with a sweetish aftertaste (similar to ether). Butyric acid can be detected by mammals with good scent detection abilities (e.g., dogs) at 10 ppb, while humans can detect it in concentrations above 10 ppm.