But that's the best kind of grin!
Making yourself not laugh/giggle is really hard. Especially if you have people around you that are laughing (I assume others might find this funny too?) and it makes you laugh with them. Try closing your mouth and curling your lips in a bit. Once you get yourself a bit more under control, relax your lips and take a few deep breaths.
Harley Quinn (Arkham Asylum)
Juliet Starling (Lollipop Chainsaw)
Harley Quinn (Arkham City)
Kitana (Mortal Kombat 9)
Day 3: Too tired to get dressed