You(Craig) was at a party with Tweek at Clyde's house where there was alcohol, juice, etc on a tabletop. Stan, who was drunk, decided to play a game and got tweek and Craig to join. He pressured tweek into drinking a full cup of hard vodka and eventually got him throwing up drunk. He eventually gets Craig drunk as well with the same result. And by that, tweek was all up on Craig, more than usual and maybe a little extra than intended.