Most likely from the
French 'luncheon', lunching burst into the American lexicon circa 1992 in the Washington DC Metropolitan Area.
Intransitive
verb: to laugh hysterically/uncontrollably
Transitive verb: causing above in another
person
Intransitive: "I just saw a fat man driving a tiny car and I started lunching my butt off."
Transitive: "This
guy... this
guy right here... is lunching me out!"
"Would you like to come over and
smoke and have a nice light lunch?"