Here's my weird pet peeve - when people shorten a phrase to the adjective that describes the noun, instead of using the noun. It's especially bothersome in a medical context.
Examples: "I have post-partum." No, you can have post-partum depression, anxiety, psychosis, hemorrhage, anemia, hypertension, etc. "Post-partum" means it happened after childbirth. If you mean you have post-partum depression, say it.
Similarly, when pregnant, "pre-natal" means before childbirth. When I was pregnant, a nurse asked me "are you taking your pre-natal?" I had no idea what she mean, until she clarified, in a tone that implied I was the idiot, "pre-natal vitamins! you have to take them!" Yes, of course I do, but I call them "vitamins." not "pre-natals" because that's not a noun.
Recently a guy told me that last year he "had a phantom." I thought her might have meant some other-worldly experience, but no, he had a "phantom heart attack." Ok, that's not "a phantom," because in that case, "phantom" is a descriptor, not a noun.
it's a trend that drives me crazy.