A recent thread got me to thinking...always a dangerous thing...about things that exist that don't seem to have any plausible reason for existing...and I'm not just talking about male nipples here...but anything you can come up with that by all sensibilities should just not exist.

I'll start: Mosquitos

Red bugs...known down here in the South as Chiggers.

Poison Ivy.

X3

The internet.

[Insert major TOS violating comment here.]
 
Ok, sorry.  I'll go with "an appendix" instead.

Directional signals on cars driven in California. 

This thread.

FSF.

Poison Ivy, yeah. And those stinkin' vines with the little black tipped spikes that seem to engulf anything around them. They seem to thrive in many of the places I need to be. I have learned to really not like them.
And my personal favorite, braille keypads on drive-up ATM's.

Chindogu- edit :actually doesn't meet the test, but great fun nonetheless.

Wasps.