Who's the biggest pain in the ass T-Pain's ever worked with? A caller asked T-Pizzle that very question on "Watch What Happens Live." The answer?

"I wouldn’t say 'pain in the ass,' but Diddy was the most what he called ‘motivating,’ and it was 'a little discouraging,'" he explained. "It was a four-day session for one song and Diddy would just push you do things that you wouldn’t normally do. He'd try to get you outside of your box."

What exactly did Diddy do?

A lot of this, according to Pain:

"I’d put one track on a beat and he’d be like, ‘That’s not it. On to the next one,’" he said. "And I’d be like, ‘Well, I didn’t…Wait ‘till I get the idea.’ But ‘Nope. Next one.’ And bam. It was just a lot of that."

Apparently, that was a helpful experience, even if it was a little discouraging.

"In the end, him being a pain in the ass kind of helped me be better with myself," he said. "With myself, I push myself the way Diddy would push me."

When asked if he ever worked with him again, though, T offered this: "I did not." And then, he hit us with the sip.

Back in 2009, Pain told MTV News that he was hiding from Puff, which sounds pretty interesting if you think about how many people actually want to talk to the Bad Boy boss.

"Diddy’s kind of aggressive," he said at the time. “He can get that way, but I tried to change my phone number every time he tried to reach me.”

Watch the full "Watch What Happens Live" vid below.