The last three months I suffered from some really serious back pain (have finally found some relief). At one point I had gone in to the ER and they had me in a double occupancy room with no door. A nurse had come in and was offering me a shot of some type of NSAID and was telling me I could have it injected either into my shoulder or my rear end. As I was mulling over where to have the injection, a cute young nurse happened to be walking by and overheard the conversation and abruptly stopped, poked her head in the room and simply said (and I believe this is an exact quote), "It feels way better in the butt, trust me!"
In spite of all the pain I was experiencing, my juvenile mind won the day and I couldn't stifle an audible laugh. I can't be certain, but I think I saw a look of recognition and embarrassment on the nurse's face as she quickly walked away.
I'm sure it's a commentary on my puerile mind, and possibly also on the need I had for comic relief in the moment, but that hit me as one of the funniest moments I had experienced in a long time.