5 Seconds of Summer played their last gig of the year Monday and things got weird on the red carpet.

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On Monday the Aussies headed to Washington D.C. for their final show of 2014 to take part in HOT 99.5's Jingle Ball.

Ashton Irwin, Calum Hood, Luke Hemmings and Michael Clifford walked the red carpet in odd attire. They as Irwin put it on Twitter are "Gramps AS F---. hahahaha". 

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The four Aussies dressed as if they were grandparents. Irwin and Hood took on the role of grandpas. Irwin held a cane while Hood sported a super thick gray mustache. Hemmings and Clifford appeared to be dressed more along the lines as grandmas than grandpas, but they definitely had the elderly vibe down. Hemmings and Clifford donned little purses, interesting scarves, beaded necklaces and more to achieve the grandma look.

The guys did an interview with the radio station's Toby prior to their set at the concert, in which they tried to explain their wacky attire.

Irwin explained, "You may be wondering why we're doing this and the answer is we don't know."

"We wanted to mix it up," the drummer added. "This is the last radio show we're doing of the year and we wanted to do something fun so we dressed up."

He also mentioned his bandmate Clifford "looks so unpleased."

After the show, the Aussies tweeted about the day overall as seen below.

Watch the entire interview below.

Tags: 5 seconds of summer