To get this set up a local multiplayer game. ( Insult a human - insult on a couch).
I got this on the pet shop level in an argument between Shufflebottom and Nigel. Its a two word phrase split between.
You, still use windows vista.
Just get the first part of the phrase then keep hittin (...) until the second part shows up. The achievement will still pop no matter which character says the phrase.