Paul Pierce is NOT sorry for posting a bunch of booty-shakin' women on his Instagram Live earlier this year ... saying he was just having some harmless adult fun.
The 43-year-old NBA legend posted a kinda NSFW video from inside a friend's home after a night of drinking and smoking back in April ... showing a group of barely-clothed ladies twerking and dancing.
The video went viral on social media ... and ESPN parted ways with The Truth shortly after.
Now, Pierce is opening up on the days following the incident .