The holy s**t moment occurred Friday as the Delta flight was headed to Barcelona, Spain after taking off from Hartsfield-Jackson Atlanta International Airport in Georgia.

While the jet was over Virginia, the passenger's gastrointestinal issues exploded out in the open ... giving everyone on board a front-row seat to the disgusting aftermath.

The flight captain radioed Air Traffic Control to report the incident and he seemed pretty calm under the circumstances.

You can hear him on the recording say, "It's just a biohazard issue, we had a passenger who had diarrhea all the way through the airplane so they want us to come back to Atlanta."

People on the flight were horrified and complained about it on social media.

One person wrote, "My partner was on that flight! It was pretty bad. It was dribbled down the aisle, smelled horrible."

Another said, "The vanilla scented disinfectant used on it only made it smell like vanilla s***."

A third called it "a mess," but praised the pilot for making the right decision to turn back around and land.

Delta issued a statement, "Our teams worked as quickly and safely as possible to thoroughly clean the airplane and get our customers to their final destination."

No word yet on the condition of the passenger.