General made up insult. If someone was to call it you, they would be saying that you are an oddly shaped penis. This is more of an insult that you would call your mates.
Friend 1: "Don't you think that mushroom and willy are weird words?"
Friend 2: "yeah if you say so"
Friend 1: "like omg we should totally call each other a mushroom willy"
Friend 2: "ok, if you want"
Friend 1: "totes amazeballs"
When someone is giving you a blowjob, and then you before you ejaculate, you pull out, and then stick the tip of your penis in their ear and then ejaculate
Adam told his girlfriend Lindsay that he was going to give her a wet Willy, but instead he gave her a RussianWilly