Whoever said you shouldn't mix business and pleasure was obviously full of it, because there are a ton of musical collaborators out there who also seem like pretty good pals. Skipping in the sunshine, sharing milkshakes, twerking all up on each other — you know, best friend stuff.

In honor of #BestFriendDay — which has been trending on Twitter over the past few days, oddly enough — MTV News has compiled what we think were the five best pal pairings from this past year.

Miley Cyrus & Mike Will Made It
Not only did Mike Will Made It executive produce Cyrus's much-hyped BANGERZ record, but Miley was also featured on Mike Will's track "23," off his upcoming album, Est. in 1989 Pt. 3 — and quite prominently in the video.

The duo seems to have become fast friends over the year, with Mike Will soothing Cyrus's nerves over the success of "We Can't Stop" — over the phone, as besties do. And rumors spread that the two are involved, which weren't helped by the two's racy Terry Richardson photoshoot. Still, a rep for Mike Will has abolished those whisperings, saying: "It is all about the music."

Even without the "with benefits" attached, however, Miley and Mike seem to have a friendship that can't stop, won't stop.

Daft Punk & Nile Rodgers
Rodgers and the robots' friendship bred one of the top songs of 2013, but, in the end, the trio's bond was about more than just "getting lucky."

"We had such a great time making the record that we bonded in such a way that's probably, you know, a lifelong bond," Rodgers told MTV News at the VMAs.

What's robot language for "Awww"?

Lady Gaga & Jeff Koons
"One second I'm a Koons, then suddenly the Koons is me," Mother Monster sings in "Applause" — a sentiment that was made literally manifest when she revealed her ARTPOP album art, which features a statue created by Koons of Gaga, incorporating aspects of his previous work.

These two make for the most a-musing muses ever.

will.i.am and Britney Spears
When pal and collaborator will.i.am confirmed that he would be executive producing Britney's new album, the upcoming Britney Jean Spears, he said, "I was like, 'OK, look, guys, me and Britney need to have lunch four times a month for three months before I even try to go in the studio with her.' Because we need to talk."

Sound like quite the grind — of fun. We're guessing that in this case "Work Bitch" would be a term of affection.

Katy Perry and Bonnie McKee
Longtime Katy Perry songwriter and musician Bonnie McKee is more than just Perry's pal — she's something much more. "Katy and I are really similar," she told MTV News. "That's kind of how we became friends. We met at Wasteland on Melrose [Avenue in Los Angeles], a thrift store. We just are totally on the same level... We're just soulmates in that way, I guess."

This calls for matching bracelets, no doubt.

Eminem and Rihanna
Eminem and Rihanna first hooked up on "Love The Way You Lie," then, mostly, recently, they teamed up once more on Marshall Mathers's new track "Monster," off The Marshall Mathers LP 2.

Looks like this ornery "rap god" has enough room on his cloud for one more.

Pharrell Williams & Everyone
From Miley to Robin Thicke to Daft Punk, Pharrell Williams is spreading the collaboration love around this year, helping many a musician score a chart-climbing hit.

Yup, a friend in Skateboard P is a friend indeed.