TheĀ Sex On Shrooms tee design is for the adult Mario fans that want him to get the princess and high "score".
Video game characters in adult situations is nothing new and neither is a Mario and Princess Peach version. But this one in particular is drawn quite well and the design is funny. The Super Mushroom as a sexual aid perhaps as a Nintendo Viagra is hilarious in itself. Let's just say that everyone is glad that Mario is facing the other way. There is also a full color version of it available.
As for the artwork, it is clean and cartoony of course. This version has great contrast and nice simple coloring. The shading is awesome with the light shining in from behind him through an implied doorway. The full color version has even better coloring.
You can almost hear "Bow Chica Wow Wow" music. One thing is for sure, if that is how Princess Peach looks I'd be risking my life to save her over and over and over again too.
This is a fun and lighthearted ADULT design to be worn anywhere where other adult gamers congregate.