A fun-vacuum: somebody with the ability to suck every ounce of fun out of a room, whether intentionally or not, at the most inopportune of times.

To alert others of the presence of a vafuum, one may make the sounds or mime the actions of an invisible vacuum cleaner sucking up the fun. It is also commonplace to ask others to lift their legs/arms up, because there's a bit of fun hidden under there that the vafuum missed on its first pass.

An extreme case of vafuum-ing is known as a MOAV - Mother Of All Vafuums.

When you eat dirt for the first time and leave your family to build a shack in the woods