Holding in a Laugh till you can't hold it any longer.
Taking a drink of coffee and someone makes you laugh, but despite your best efforts the bomb goes off and the coffee is sprayed all over.
When you read something hilarious on Reddit, and you have your pissed off sleeping girlfriend next to you, and you try not to laugh to not wake up the tyrannosaurus rex, it's like your body starts to build a laughter bomb in the bottom of your stomach, that you can no longer contain, eventually letting out bursts of loud gasping giggles while you try your hardest to keep it in. But the harder you try, the bigger it grows. The funnier it gets.