Use any one of the numbers listed on this site (making sure they've been verified first). They ALL swear. A clever troll strung out for any length of time takes practice, but if you're just starting out try something simple like:
Certifiable Teknishun: "Hello sir, my name is John Smith. How may I help you?"
You: "Hello. And how are you today, you filthy cock-sucking scammer? A thousand dicks in your father's asshole!"
That will probably get you an instant nuclear meltdown