Bad Santa: John Mayer Photo Tweeted By Katy Perry

Katy Perry was definitely feeling the holiday spirit on Christmas.

As was her boyfriend John Mayer, Santa costume and all.

Katy Perry and John Mayer spent the day at home with her parents in Santa Barbara, and the "Wide Awake" singer gifted her 30 million followers this gem of a photo.

"Santa Baby" reads the caption. You may hurl on cue.

It's the most public display of affection yet for Katy, who has been dating the 35-year-old himbo crooner for about five months (including a brief August split).

Could be the first of many, too.

"They are seriously in love and exclusive," a pal says of Perry's first long-term romance since she and Russell Brand finalized their divorce this summer.

"John is surprised at just how cool and smart she is, while John has proved he's matured and learned from his mistakes ... Katy is blown away."

Hopefully she made Santa's nice list this year, otherwise this naughty fellow might deposit some sexually transmitted diseases in her proverbial stocking.

In other Saint Nick Impostor news ... a grey Santa outfit angered a guest at a Swedish spa and conference center Tuesday. Wrap your head around that.