Noun:
an affectionate term used to refer to close friends and people you are very comfortable with. Usually in circumstances where the person using the term is trying to express affection either purely and with puppy-like playful affection or with an ulterior motive to try to get the person they're talking to to do something for them.
Person 1: Poopstix, could you possibly pass me that bowl?
Person 2: Well of course! But only because you asked so nicely!
A very prudish uptight person that gives no goodreason for not having any fun.
Michael refused to have a glass of wine with me because he insisted that it would give him a horrible headache and that he needed to get to bed before 8:00 p.m. anyway. Michael is illustrating poopstain like behavior.