Laughing so hard that you lose all restraint and laugh like a muppet, tossing your headup and down and either rubbing your belly or flailing your arms.
Nick's fart was so loud I couldn't help but do a muppetlaugh.
1. Accepting the term "Muppet" to denote a persons total lack of basic common sense, this logical extension would suggest that, whilst the subject approximates to the qualities and ideals of muppethood, inclusion in the "Muppet" category would require significant mental development.
2. A retarded muppet.