Oh...Sir! The Hollywood Roast

This is unlocked by playing, and completing, online matches only. Offline single player and local co-op matches don't count, even though there is an offline mode called 'Scenes'.

This achievement will unlock as soon as you have completed your 25th match online.

*EDIT* A good method to achieve this quickly is to find a boosting partner, have the first player press B to end their turn and for the second player to run the clock down until the health bar is fully emptied. It is possible to speed this up by 15 seconds by getting a poor grammar penalty. Thanks go to Conor x420a for suggesting this method.