Dancing the night away with Cameron Diaz and Leslie Mann will do that for you.
"It was the best way to celebrate," says Upton, laughing. "It was big party!"
The model has her first major film role in the new comedy The Other Woman. "We knocked it all out," chimes in her prolific 41-year-old co-star, Diaz. "It was a 12-hour dance party. We really showed her just what it's like to be an adult, a proper adult!"
Today, there's no dancing to be done but the three women, squeezed onto a small sofa, seem effortlessly at ease with each other, with arm patting coming thick and fast.
Aside from the birthday bash, Mann, known for her comedic roles in This Is 40 and Knocked Up, says that she and her two co-stars made sure they had plenty of "dinners together and some long talks" before the cameras rolled.
The film sees Mann play Kate, a woman whose confidence has faded after years being married to narcissistic husband Mark King (Game Of Thrones star Nikolaj Coster-Waldau).
When she suspects Mark has been having an affair with lawyer Carly (Diaz), she decides to confront the other woman. But when she does, she realises that Carly has also been duped by Mark, who hasn't told her that he's married.
An unusual friendship strikes up between the two women, who are determined to right Mark's wrongs - especially when they discover that he has been cheating on both of them with younger model Amber (Upton).
It was the opportunity to show that female friendship in films can be supportive, and not "catty" that grabbed Diaz.
"Our objective here is to show that women don't have to be at each other's throats, you know?" says the Californian-born actress. "That's a beautiful thing. It's about friendship and about women.
"What I also loved about the script is that it wasn't man-bashing or about revenge. It's about a journey that these women take with one another to learn about themselves."
In real life, all three women agree they would advise their own friends to end their relationship, if they found out their partner was a serial cheat.
"Let it go, move on, you can't change them," says Diaz, looking to her two colleagues. "You can't change who they are. Get out of there."
And like their characters, the actresses have relied on their own friendships to sustain them throughout life.
"My friendship with my girlfriends means everything to me," adds Diaz, who is currently single. "I spend more time with them than I do anybody else. Through the hard times and the good times, all of them."
Mann, who is married and has two daughters with Judd Apatow, the director of comedies Superbad and The 40-Year-Old Virgin, agrees.
"I've had the same best friends since I was in middle school," says the star, who met Apatow on the set of 1996 Jim Carrey film The Cable Guy.
"I love them so much. We do these hotel days where we start as early as the hotel will let us in, so like 10 or 11 in the morning, and we talk and talk and talk until 1am the following morning, drink a lot of wine...
"We get so much off our chests. I love it, I don't know what I'd do without that day with my girlfriends."
And it looks like Diaz and Upton might soon be joining that throng of friends.
"There are certain people who have an ear for comedy. It's like a song and a rhythm, so when you're doing comedy, if the other person isn't hearing the same thing as you are, it just lays there and dies," explains Mann.
"Cameron hears the same thing as I do. We can pick up where the other one left off and it's a good give-and-take. And Kate Upton has that, too. She knows how to play things and she's super-smart."
"We fell into a nice rhythm together at work, and bonding naturally happened easily."