An event when an individual tries to urinate and comparatively insignificant amount of urine is expelled out of the body (less than 50 ml usually).
Man to a Friend: I woke up last night really needing to take a piss. After forcing my tired ass to the loo only a few drops of piss came out.
Friend. It was only a pee-diddy. Don't worry about it.
"I usually end up doing a pee-diddy just before I undertake a sporting activity. I just have to get all the liquid out of me to feel comfortable on the field."