A gesture used to relieve the tension of an awkward situation.
The awkward salmon is usually performed when sitting, although it can be done standing. The person spreads his legs slightly apart and puts his hand in between them close to the knees. Then he rapidly moves his hand back and forth slapping each leg to simulate the sound of a salmon flopping around on the ground.
The awkward salmon can become even more awkward (and a lot funnier) if a person sneaks up behind another person and performs the awkward salmon on the victim.
Grandma: Damn your grandpa is good in bed.
Grandson: (to his friends)... AWKWARD SALMON!