"Oh, God! Don't even start! All my celeb friends!" Schumer joked, before adding, "She's the coolest chick you'll ever meet. She's beautiful."
The "Trainwreck" star, 34, then revealed how she ended up vacationing with the "Hunger Games" star, 24.
"Once a year I go away with all my girlfriends from high school. We went to the Hamptons because they wouldn't let us go back to Martha's Vineyard. No one would rent us a house because they heard about us," Schumer said, without elaborating why.
"So we go to the Hamptons, and Jennifer and I have become friends. I was like, 'Oh, we're going on a boat tour tomorrow. You should come.' It was kind of a hypothetical," Schumer said. "And she was like, 'I think I'm coming!' I was like, 'Oh, my God!'"
The best part, though, was seeing her friends' reactions, which Schumer actually filmed.
"They're like nurses and teachers, and I'm like, 'Jennifer Lawrence is coming on a boat with us tomorrow,'" Schumer recalled. "They're all screaming!"
So how did Schumer end up on the back of a jet ski with JLaw?
"We wound up going jet skiing and I was like, 'I'll drive! I've got this!' And she was like, 'No, I'm Hunger Games,'" Schumer explained.
A photo Schumer posted of the pair with the caption, "Jlaw #maniac," got close to 40,000 likes.
There's also a photo of the women forming a human pyramid...
And chilling on some big floaties. Schumer captioned that one, "Binders of women."
Schumer offered Stewart an explanation for why the photos went viral.
"It's my picture next to Jennifer Lawrence's -- like the last person you want to be next to," she said.
Schumer then joked, "I look like her coach in all the pictures. I look like I'm telling her to take a knee, like, 'Listen, Jen!'"