uninvited guest 

another name used for an unexpected erection gained while in a difficult social situation

one might suffer an uninvited guest during class due to the female classmates attire (or lack thereof) and needs to concentrate on other non sexual feelings in order to calm 'the beast within'

uninvited guest by SoosterFly December 21, 2010

Uninvited guest 

When a group of people enter a bathroom and consecutively defecate into the toilet without flushing. Best when done with a dry dock.

We all went over and left an uninvited guest at their house.

Uninvited guest by CharlieMacDeeNDennis January 13, 2009

uninvited guests 

Any creature that chooses to make its home in a hard to reach area in your house. Be it in the attic, basement or inside a wall, these guests are often rodents, reptiles, or insects of varying sizes. Once discovered, uninvited guests are very hard to evict from your home.

I've placed some rat poison in the attic and sealed up any holes in the walls so we don't get any uninvited guests trying to make their homes here.

uninvited guests by Dan April 21, 2008