Megan Fox Posts Sexy Photos After Blocking MGK on Instagram

Megan Fox is learning what life without being bothered by her ex, Machine Gun Kelly, online is like ... posting more sexy snaps to Instagram after blocking the music star.

The actress threw on a tiny skirt and a tight white shirt in these pics ... bending over on top of a bed while taking notes -- with some NSFW photos, including one seemingly showing two people engaged in some adult action, laid out in front of her.

Fox seems to be harkening back to the naughty schoolgirl days of the early 2000s -- think Britney Spears in "...Baby One More Time" -- complete with the pleated skirt, long socks, and pigtails.

She's got cherries displayed prominently on the front of her shirt ... and she captioned the snap, "it is double pleasure to deceive the deceiver."

The quote -- attributed to Italian political philosopher Niccolò Machiavelli -- is all about manipulating a manipulator ... and could be a dig at MGK.

As we told you ... Fox transformed her IG into an MGK-free space, with sources telling us the two have no relationship outside of co-parenting their daughter, Saga.