Blake Shelton and Adam Levin
Blake Shelton (left) has been poking fun at Adam Levine (right) on Twitter for shaving his head bald. Here the two singers attend NBC's "The Voice" Season 7 red carpet event on Nov. 24, 2014, in Universal City, California. Getty

"The Voice" coaches Blake Shelton and Adam Levine never shy away from making fun of each other. Not only do the two singers go back and forth on the NBC competition show, but their jabs often spill over onto Twitter. Shelton has not held back from making bald jokes ever since Levine made his debut on the show with his shaved head Oct. 12.

Shelton took to Twitter Monday and throughout the weekend to share several pictures of bald Levine, 36, next to characters the Maroon 5 singer looks like. This included Squidward from "Spongebob Squarepants," Voldemort from "Harry Potter" and Casper the Friendly Ghost.

Despite the constant Twitter jabs, Levine has yet to fire back at the country singer on Twitter. Levine's last post was Oct. 12 when he responded to the 39-year-old's suggestion that he now looks like "Superman" villain Lex Luthor. Shelton had tweeted at Levine and fellow "Voice" coach Gwen Stefani earlier, saying "Thank goodness #Gandhi was there to help you make that decision, @gwenstefani #AdamsBald"

Levine may not have answered Shelton yet, but the singer has not been afraid to send joking insults to Shelton on Twitter as well. On Sept. 21, Levine posted a tweet doing an impersonation of him.

"The Voice" returned to TV Sept. 21, and the two judges wasted no time in continuing their friendly rivalry. In an interview with E! Online, Shelton immediately took a shot at Levine's current lack of hair.

"If I ever wanted to go out of my way to look like a complete idiot, I may shave my head like Adam," Shelton said. Levine later respond to Shelton's comments to Carson Daly, saying: "Blake must've spent 10 hours researching jokes about every famous bald, evil person in TV and film, and breaks out the references." According to the Huffington Post, Levine's hair has already grown back since the summer.

Shelton and Levine have been a part of NBC's "The Voice" for all nine seasons while still remaining active in their musical careers. Although there's a lot of back and forth, the two are real-life friends.

"The Voice" airs on NBC Mondays at 8 p.m. EDT and Tuesdays at 9 p.m. EDT.

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