BEVERLY HILLS, Calif. — Drama class was an easy A for actor Michael Rosenbaum. He wasn’t in it for the glory or the attention. In fact, he didn’t participate in any of the plays at first. “I was taking drama classes but I was still nervous and shy, and my teacher said — I was a senior — she said, ‘Listen, you can’t take Drama 4 unless you audition for a play.’

“To me it had been an easy A. You just got up there and read some plays.” Reluctantly he agreed to audition for “Grease.” “Doesn’t every actor audition for ‘Grease’?” he said.

To his surprise he landed the part of Vince Fontaine, the teen dance-show host. “‘Hey, hey, this is the main brain, Vince Fontaine, spin the sacks of wax here at the house of wax, WAXX,’” Rosenbaum recites. “I still remember because I was soooo nervous.”

It seems a light-year leap from Vince Fontaine to Lex Luthor, whom Rosenbaum portrayed for 10 seasons in “Smallville.” With his shaved head, and coolly malevolent stare, Rosenbaum forgot all about Vince Fontaine and his teenage patois.

It’s another seismic revelation to find him playing a spirited con-man with a full head of hair, 5 o’clock shadow and peerless comic timing in TVLand’s “Impastor.” He portrays a street-wise grifter who suddenly finds himself heading a devout congregation which mistakes him for their new pastor.

He says he’s not nervous anymore.

“If you knew me in high school, I was the shortest kid in high school. I didn’t start puberty till late. I didn’t have many friends. I like to call myself ‘ahead of the times.’ The next morning (after “Grease”) I was walking down the hallway and a couple of the popular kids said, ‘Hey, you’re pretty funny.’

“So for me, not being me, on stage I could be any weird, eccentric — anything I wanted to do on stage, I could do. I didn’t feel like I was being judged. It was MY time. And I built slowly through college, doing more plays and off-Broadway. I started to build more confidence and suddenly I started to realize, ‘Hey, you know what? You might have a career in this!’”

There were people along the way who encouraged him. Among them was his maternal grandmother, Ruthie. He wears a tattoo on his arm in her honor. “You need somebody — your grandmother or somebody who believes in you,” he says, his hands resting on the glass-topped table.

“She was one of these people who had a lot of money. All of her money she spent taking care of her family in her later years. That eventually drained her account. She sat down one day and said, ‘Don’t blow your money because people always need money when you start having it.’

“She said, ‘You’re the only one that listens to me.’ … I wanted to hear her stories. We’d sit around and talk for hours. I filmed her and interviewed her about her life. She was tough. She wouldn’t put up with anybody’s s—. I learned how to be tough from her.”

Rosenbaum was in his late 20s when his grandmother died. “Grandma’s death made me cherish the important things more,” he says.

“Made me want to spend more time with my friends and loved ones and be happy and (understand) what really counts in life. Because when you’re on your death bed and you’re 95 years old you shouldn’t judge your career based on success, but it’s the people who are always there by your side; the friends, the great moments. It’s about the human connection, those little moments,” he pauses.

“My grandma’s death made me think more about life. People die around you and all of a sudden the world stops and it’s amazing how it takes you back to reality. People say, ‘Do you get over someone’s death?’ You never get over it, you just learn to live with it.”

Though he’d like to marry and have a family, Rosenbaum says he hasn’t met the right girl yet. “For me. I had a little dysfunctional family, and for me I always look a little too closely at red flags. I go ‘ewwwwwww, that makes me think of certain things when I was younger.’ Eventually I want to have a family, find somebody who’s patient with me. The last girl I went out with was a teacher from Montréal. She was a great girl but she was too far away. But I don’t give up.”