“The main reason for doing it was Melissa McCarthy. I had seen her in ‘Bridesmaids,’ and I wish I could be as clever, wonderful and physical in comedy as she is,” Bates told me in a recent interview. “I wanted to get to know her — I really wanted to understand her secret. I wondered, ‘How can she stay so real yet push the envelope the way she does, physically and comedically?'”

Bates said she still doesn’t have the answer to the mystery, but she at least has a better understanding of who McCarthy’s gifts mirror.

“I can see a comparison in her and Lucille Ball in the way Melissa fearlessly goes places that a lot of actresses wouldn’t go,” Bates said. “She’s nimble, quick and fearless. ”

Bates added that being around McCarthy encouraged her to up her comedic game — or at least try to up it.

“It was wonderful to pretend for a while that you can be as funny as she is,” Bates said, laughing. “When we were all doing our improv scenes for the film, we were just shameless trying to be as good as Melissa because she raises the bar — but of course, we fell short.”

Opening in theaters nationwide on Wednesday, “Tammy” stars McCarthy as the title character, a down-on-her-luck fast-food worker whose day starts off with a deer-car collision and quickly spirals out of control from there. There appears to beacon of hope, though, when her hard-drinking, foul-mouthed and sexually liberated grandmother, Pearl (Susan Sarandon), bankrolls a well-intended road trip that quickly detours into disaster.

Bates stars as Lenore, Pearl’s cousin who provides safe harbor to Tammy and her grandmother when Tammy runs into trouble with the law.

Apart from working with McCarthy, another first for Bates working on “Tammy” came with throwing a Molotov cocktail, which is featured in a scene where she’s helping conceal some evidence connected to one of Tammy’s many misgivings.

As Bates discovered, tossing the flammable firebomb was fun — and a bit dangerous.

“That was really a blast, I have to say,” Bates said with a chuckle. “I held one a little too long and it exploded in my hand. It was sugar glass, so you really had to throw it quickly once the end of the cloth was lit.”

Fortunately, Bates wasn’t hurt in the incident (“It caused a tiny nick from a sharp corner of the sugar glass,” she said), making her Molotov cocktail-throwing endeavors all the more enjoyable.

“It was fun to blow up shit or pretend that you were blowing up shit — and not be arrested,” Bates enthused.

In addition to playing opposite McCarthy, Bates said she was also excited to work under the direction of Ben Falcone, McCarthy’s husband and co-writer on the film. Falcone, of course, has also worked often with McCarthy as an actor, too, in such films as “Bridesmaids,” “The Heat” and at the beginning of “Tammy” — and Bates believes his experience as an actor was not only beneficial to his creative partner, but to the whole cast.

“Ben had been with the script for six years and he knew how he wanted to shoot the film and the story he wanted to tell,” Bates said. “Being an actor is really a major plus in his makeup as a filmmaker, because a lot of younger writer-directors haven’t a clue how to talk to actors. But because Ben knows acting so well, he knows when to say something and when to shut up. He also knows when he’s got a shot. He doesn’t have to play it over and over from the beginning until the actors are exhausted and don’t know what the directors want.”

Bates, who stars with Sandra Oh as a lesbian couple in the film, also appreciates the way Falcone presented the healthy relationship of the couple, which is revealed in a pivotal scene where Lenore in a tough love sort of way explains the hardships of life.

“In the scene, I wanted Lenore to talk about the difficulties 20 years ago of being in love with a woman, starting a business , trying to get to know people in the community and have a normal relationship with them,” Bates, 66, recalled. “Straight people in those days were probably ill at ease, of course, and others more accepting. So in the case of this film, to have two gay women build up this business and have the healthiest relationship of all of them, was inspiring. There were no caricatures. There was tremendous love.”

Another relationship examined in the film is the family dynamic between Lenore and Pearl — and Bates said she couldn’t have been more excited than to play cousins opposite Sarandon.

“I was very gracious to have scenes with her. The film really gave me my first chance to do scenes with Susan, even though we were both in a film with James Spader called ‘White Palace’ where I played Jimmy’s boss,” the “Misery” Best Actress Oscar-winner said. “I was very green as a film actor back then and was very much in awe of Susan. Still to this day for me, ‘Thelma and Louise’ is right up there as one of the most wonderful movies ever made. Susan’s and Geena Davis’ performances in that movie really get to the heart of women’s rage.”

Apart from Sarandon’s screen work, Bates said she loves how Sarandon “puts her money where her mouth is, politically, when it’s not fashionable to do.”

“She’s very well-versed about what’s going on in the world with global issues, so I’ve always admired that trait in her,” Bates said.