Kacey Musgraves Curses at Fan Who Grabs Her Mid-Performance, Video Shows

Kacey Musgraves' show Friday night wasn't all 'Butterflies' and 'Rainbows' ... 'cause a fan grabbed her mid-song -- and, video shows she was pretty pissed.

The singer-songwriter brought her "Deeper Well" world tour to the Amalie Arena in Tampa, Florida ... performing her hits to a packed crowd, when she got a little too close to an overeager fan.

Watch the clip ... KM's in the middle of playing a song when a fan reaches out and grabs her roughly -- basically spinning her around.

Musgraves takes the microphone away from her mouth and appears to say "What the f***?" to the fan before shaking her head and moving on.

A consummate pro, Kacey didn't make a lot out of the moment and kept the show going ... but, you can tell she was pretty pissed about the scary moment.

It's unclear if the person who grabbed Musgraves was booted from the venue ... though some online are claiming that's exactly what happened.

Of course, singers have been dealing with unfortunate fan actions a ton in recent days ... with Zach Bryan pausing his concerts on two different occasions after getting objects thrown at him and Kelsea Ballerini taking a bracelet to the face last year.