The actors stopped by Busy Tonight on Monday to promote the film, which follows two teenagers with cystic fibrosis who fall in love in the hospital. Sprouse and Richardson tried to keep the mode light while making the movie, despite the heavy subject matter.
"I'm not the type of person that can be sad and serious for a long period of time, so, in fact, the more sad and serious I am... then when I break from that it's like extreme the opposite direction," Richardson, 24, said. "And there was a lot of long, like 20 hour, days, so we were delirious pretty much the whole time, actually, right? So there was just a lot of... antics. I actually don't know the definition of that word, but it sounds like it fits."
The pair filmed Five Feet Apart in New Orleans, which prompted the host to ask if they went out and partied after completing their emotional on-set duties. "Did we go out into the French Quarter, Cole?" Richardson questioned with a laugh and a sly smile.
"She took us on the most wild strip club tour inside of New Orleans," Sprouse, 26, revealed.
Richardson confirmed Sprouse's story, telling the audience that she felt, "like, I'm too sheltered because I was a 23-year-old woman-girl-person and I had never been to a strip club."
"We were in New Orleans, doing this heavy movie, and, like, on the weekends, all I wanted to do was get drunk and go to strip clubs," she admitted. "So, that's what we did."
While the pair seems to have had quite the time out on the town, Sprouse encountered a hilarious problem -- one that Richardson didn't even realize. "Apparently a lot of the strippers watch Disney Channel," he quipped.
"Did they recognize you?" Richardson questioned. "... I was honestly too into watching them [that] I forgot that I was with anyone. Because they're incredible... There's a way to be a stripper and it to be magnificent and athletic and incredible and inspiring."
"I think... I was like, 'How are you doing that? And you're making that much money. And you're getting a workout. And you're hot!'" she added.
While the duo started the night at female strip clubs, they closed out their experience at its male counterpart. "It was Magic Mike," Richardson said, before adding, "We didn't see any weenies."
"Alcohol and dongs are a no go," Sprouse confirmed.
"You could see the shape of wieners, but we couldn't see, like, wieners," Richardson further explained through laughter.
Despite their obvious goofiness, when ET caught up with Richardson earlier this month, she gushed about tackling the more serious parts of the project with Sprouse.
"We both just really cared about doing a good job, and doing justice to these characters, and making it as grounded and lived in as possible," she said. "Also, he's a nice, cool guy in real life, so I think it's one of those things where if both people are willing to commit to telling the story properly and believing the words they are saying, then it kind of happens."
Busy Tonight airs Monday through Thursday at 11 p.m. on E!