Someone who laughs so uncontrollably that they are unable to control their flatulence. The release of gas may lead to more laughing which then leads to another fart. Laughfarters are common amongst happy and vegetable eating societies.
When you are laughing so hard you lose control of your basic abilities, including and not exclusive to: the ability to say what you are trying to say, your ability to be understood by those around you; in extreme circumstances, you lose continence
" I understood you until you turned into a laughtard (n.)"
"I was giving my speech and my mind when blank, then I just lost it and went laughtard(n.)"