When I was in junior (maybe sr.)high school, I remember it was quite the insult to be told to "go suck a big, green weenie." At the time, I don't think many understood the connotations,

Nowadays I don't think most people even think about it re' fellatio. It's just a catchall word for when something seems wrong, unhappy, etc. as in "That sucks!" when a child is told they may not go out.:-)