1) s/p: Means status post. Meaning, something that happened. I use this so much. So much. I could use it like five times in a sentence:
Mr. Smith is a 63 y/o man with h/o CAD s/p cabg s/p fall with large SDH s/p R craniectomy s/p wound infection s/p I+D.
I really do try to limit myself to once per sentence though.
2) c with a line over it: Means "with". I use this probably more than s/p.
Husband: "What does c with a line over it mean?"
Husband: "I don't get you doctors! Why don't you just write 'w' with a slash?"
Me: "Because this is Latin!" (cum is latin for "with")
3) @: Means "at", obviously. This saves absolutely no time over just writing "at" yet it looks immensely cooler.
4) 2/2: Means "secondary to".
Neurologist: "You know what abbreviation really annoys me? 2/2. Because why can't you just write out 'due to'? Is it really that much harder?"
5) D/C: This is the greatest abbreviation ever because, especially in my field, it can be used to mean practically anything. If I wanted, I could write:
If there is no D/C from the wound, please D/C the dressing prior to D/C home.
And I did. And the nurse paged me and was like, "WTF?"