Think of the first time you saw an image of Edvard Munch's The Scream. It is truly an intriguing image that has the ability to create a feeling of awe. What is happening to this figure? What is with that expression? What is he viewing out of our line of site that is instilling him with this emotion?
In a similar manner, I feel that same wonder when I gaze upon this image. What is this chubby tub of black metal fury laughing at?

Here are my theories, please feel free to add your own.
1. His tests came back negative. He is loving life.
2. It is his birthday and he is excited because up front he sees his girlfriend walking towards the stage with a Dairy Queen ice cream cake. He is so overwhelmed with happiness at the thoughtfulness of this gesture he can't help but express his joy!
3. He is a real jokester AND he just farted. He is looking forward to hearing the "awwwwwww...man" coming from Mr. Grumpy Guitar. That dude can never take a joke, which is why he wears a frowny face.
4. Someone is flashing his balls. He loves lowbrow humor.
5. He is not in a black metal warrior at all, maybe this is a halloween show and this is a death metal band. Perhaps he is laughing because he realizes how absurd it is to be in a black metal band.
Regardless of all this, if you know what this is actually from please keep it to yourself. Don't ruin my fun.