What's the worst trait to have?

[Hikamaru]

^ I second what Skymin said.

Basically having an arrogant nature which can put you in such sticky circumstances, and given the fact I fail at real life social stuff it can make me feel down. It happens to me a lot, having an arrogant nature.

 

[Crux]

^ All of these are pretty terrible traits... but.

I'd have to say being way to serious.
Taking yourself to seriously easily leads to ego, apathy, selfishness, narcissism,etc.

"Life's to short not to laugh."

 

[PlatinumDude]

Arrogance is the worst human trait, IMO, since no one really likes being with an arrogant person.