The Vomit Comet is the nick-name of the 300 Bloor-Danforth Blue Night Network bus route.
It's not hard to guess why...
The 300 and 300A provides after-hours bus TTC service when the Bloor-Danforth Subway is not running.
Likewise the 320 Yonge bus route retraces the Yonge Subway line.
Last Call for alcohol is 2 a.m. and the Subway System calls it a night at half past the hour.
It happens now and then that riders on this route happen to vomit their alcohol an/or cookies in-between stops onto the floor of the bus itself. Blue Night Network bus drivers at times have a hurry up and wait style of rocketing from stop to stop.
Put those two together and we get the Vomit Comet moniker.
YouTube: Drunk Bus Fight on the Vomit Comet, 23 September 2007