Shaquille O'Neal Admits No. 2 Emergency Sparked Abrupt 'Inside The NBA' Exit

Shaquille O'Neal is clearing the air on his infamous bathroom emergency on "Inside the NBA" last month ... admitting once and for all he had to take a dookie.

Yes, someone is getting paid to write this.

The NBA legend let it all out during his appearance on "The Tonight Show" with Jimmy Fallon on Thursday -- after initially insisting his rush from the TNT desk was to drain the snake, he revealed it was a dire situation involving clenched butt cheeks.

53-year-old Shaq started off his explanation by saying he drank a lot of water that day ... and even though he displayed a "No. 2 run," it was not how it seemed.

But the four-time champ couldn't keep up with the lie ... and told Fallon he really had to drop a bomb.

"I just made a mistake," Shaq said. "I lied to you on national TV. It wasn't a No. 1 run -- it was a No. 2 run. I had to go bad. I had to go so bad."

"Did you see me squeeze my butt cheeks when I was running??"

Of course, his cohosts made sure to troll him over the whole ordeal ... and even brought in a portable toilet to help him out the next night.

Shaq also got offers from several adult diaper companies ... which told TMZ Sports at the time they wanted to hook the Big Fella up with some product.

Shaq blamed it all on his olive oil cleanse ... which, along with the belief it helps shrink the stomach, apparently has a side effect of REALLY clearing someone out.

So why put himself through such an experience?? Shaq said he wanted to be sexy.