As a student I crushed a K-Dur (potassium) tablet and put it down an NG tube. I didn't realize the K-Dur wouldn't dissolve and it ended up clogging the tube Oh, and this happened in the middle of the night. I dreaded having to call the Dr. in the middle of the night for a new order to re-insert the NG and have to admit my stupid mistake but fortunately (for me) the pt. ended up pulling the tube out shortly afterwards and then I had a legitimate reason to call.
Another time a nurse told me to give pt. xxxxxx a "20mg Bentyl injection." Well I didn't bother to check the order myself and I ended up giving it IV instead of IM. Bentyl is not indicated for IV use...it can cause a thrombosis and/or embolism when given IV. Had to write that one up and kick myself later.
I always remind myself that 1) always follow the five rights, 2) you can never get vital signs too often, 3) when in doubt, stop and find out first and 4) know your institution's policies!