Derived from the phrase "twat munch" a synonym of "muff diver", cunnilingus, etc.
Has come to mean a offer of luncheon to a male friend or work colleague (it's believed this started due to the bewildering array of pretty ladies seen in summer months while on lunch breaks), however it still retains its original meaning when relating to a lady.
"Hey Bob, i'm starving... Twuntch?"
A:"Where have you been?" B:"Just getting twuntch."
"She's so hot, i'd be twuntching on that for life - even when her mimsy goes all badger grey"
"She called me a 'horny savage', i'm guessing this was due to my twuntch technique"