to accidentally and unnecessarily harm yourself through pure stupidity. For example, bringing a loaded, unregistered, illegal handgun to a public place and shooting yourself with it. From Plaxico Burress, NY Giants wide receiver.
as a noun:
"I pulled a real plaxico by trading DeAngelo Williams. Now I have no RB's!"
as a verb:
"Why did I plaxico myself by planning on starting two Cleveland Clowns in the fantasy playoffs?!?"