a phrase made redundant because "shiitake" means mushroom in Japanese, there for it doesn't mean "Japanese mushroom;" it actually translates into "mushroom mushroom."
1: What does shiitake mushroom mean?
2: Dude, it means "mushroom mushroom."
1: No seriously, what the fuck is shiitake??
2: Just shut your ass.
When you're hitting a chick back door and you pull out a poop dick. Then turn her around and mushroom print her forehead with your poop dick.
I remember this girlfriend from back in high school. I found out she was banging my dad, so I gave her the Shiitake Mushroomand dumped her!