I have came across a list of emotions after the jump that can be used during the avatar creation process. These can be used to create a really cool gamer picture. If you have discovered any that aren’t detailed below, please feel free to share.

While in Avatar Customizer

Left Bumper – Makes Avatar do a random expression: depressed, apologetic, surprised, laughing, or angry.
Right Bumper - Opens Avatar’s mouth
Hold Left or Right Trigger - Spins Avatar making it lose its balance.
Move Right Thumbstick - Rotates Avatar’s head.
Move Right Thumbstick Left, Right, Left, Right – Makes Avatar angry.
Move Right Thumbstick Up, Down, Up, Down - Makes Avatar happy.
Rotate Right Thumbstick in a Circle – Makes Avatar dizzy.
Click Right Thumbstick – Makes Avatar burp.
Hold Right Thumbstick Left then move Right – Makes Avatar enthusiastically spin.
Move Right Thumbstick Up then Down - Makes Avatar hit its head on the screen, making it dizzy.

While in Xbox 360 Dashboard

Move Right Thumbstick – Rotates Avatar’s head.
Move Right Thumbstick Left, Right, Left, Right – Makes Avatar angry.
Move Right Thumbstick Up, Down, Up, Down – Makes Avatar happy.
Rotate Right Thumbstick in a Circle – Makes Avatar dizzy.
Click Right Thumbstick - Makes Avatar smile and wave