[Screaming_Gerbil]

...ethanethiol (Ethyl Mercaptan)...

I looked up "Ethyl Mercaptan" and it seems that is the stuff they add to natural gas to make it smell bad as a warning indicator for gas leaks.

I think you may be referring to "Butanethiol".

http://en.wikipedia.org/wiki/Butanethiol

Doing a bit of online searching for chemical stink bad odor practical jokes I found this stuff available.

Seems to me not a very funny practical joke, but something worth knowing about in case of being in a situation where this smell has suddenly appeared and knowing that this stuff is available for some practical joker or anarchist type to use to disrupt operations in / deny access to an area.

[Gorzaloon]

looked up "Ethyl Mercaptan" and it seems that is the stuff they add to natural gas to make it smell bad as a warning indicator for gas leaks.

I think you may be referring to "Butanethiol".

The local nerd had ethyl. It does not hang around as long as some of the others. n-Butyl Mercaptan is natural skunk juice.