I just love stuff like this.
From Erin McKean, I learned about sweet tooth fairies, “a combination of two two-word phrases that, when overlapped, make a certain cockeyed sense. Sweet tooth + tooth fairy = sweet tooth fairy.” Some examples include: drag queen bee, peer pressure party, and victory lap dance. Check out “Sweet Tooth Fairies: The Rise of a Language Mash-up.”
For more like these, you’ll want to check out the Illustrated Sweet Tooth Fairy, website of Graham Hidderly/Burgess (yes, it’s a slash), who coined the term in 2008.
Also, you’ve heard of words such as trim (which can mean both to remove or to add), screen (which can mean to show something or to conceal something), or cleave (which can mean both to split something and to cling to something), these are words that also mean their own opposite. Crazy. Also called contronym, contranym, and auto-antonym, I was delighted to learn the more whimisical term Janus words referring to the Greek god with two faces, one that looks forward and one that looks backward.
(As an aside, once upon a time, a fellow English grad student named a cat who had a face that was half black and half tabby Janus. Uh, yeah, not nerdy at all. It took me awhile to get the joke. I thought they were calling her Janice.)