Painis Cupcake is a Gmod Monster created by Rubberfruit. He is extremely popular throughout the Gmod community, and he is also a common sight on Aeiou as well.
Painis Cupcake appears frequently in Robert Joe's Rant Adventures. Unlike most people, he gets along very well with Jenna, since they are both obsessed with violence and cannibalism and may have met during Jenna's days as the BLU Pyro.
A far more detailed description of Painis Cupcake can be found here.