It's a red Swingline Stapler.
Specifically, it's the inner hinge you see when you open it up to insert more staples.

Apparently, my mystery object was too easy this week. Almost everyone got it right. Pat Haughton wins the bonus points for guessing exactly that it was a red Swingline stapler, and for alluding to the cult comedy film "Office Space".
I've had this stapler since the early 80s, long before the movie came out. Now, I'll definitely never get rid of it.

"Excuse me, I believe you have my stapler . . ."