Seacrest went off on Cowell on the Fox network's singing competition after the acerbic judge called him "sweetheart."
"Don't call me sweetheart. ... We don't have that kind of relationship," Seacrest said. "I don't want that kind of relationship."
"I don't want that kind of relationship," repeated Cowell, to which Seacrest replied: "Exactly. We'll just work together, that's fine with me."
Later in the two-hour broadcast, Seacrest continued to needle Cowell, who was harshly grading the 12 male singers vying to win the "Idol" title and a record contract.
"Why are you being so negative tonight? I mean, you've been very, very negative," Seacrest said.
"I'm not being negative," Cowell replied. "Unlike you, I actually respect the audience at home and I don't — and I don't believe in lying to them."
That didn't appear to go over well with Seacrest, who closed the sing-off by thanking Randy Jackson, Paula Abdul and the band — but not Cowell.