Robby Anderson -- the guy who allegedly told a cop he was going to find his wife and bang her out of spite -- is essentially off the hook in his speeding case ... and all he had to do was pay a fine!!!

Remember, the NY Jets stud WR was arrested in Florida back in January after cops say he was doing 105 mph in a 45 mph -- and during the stop, he went completely nuclear on the arresting officer.

"He was going to find my wife, f*ck her and nut in her eye," the officer wrote in his arrest report.

Anderson was initially hit with 9 charges including 3 felonies (harming a public servant, fleeing and eluding and reckless speeding) and faced up to 15 YEARS in prison!!!!

But now, the Florida State Attorney's office tells TMZ Sports ... prosecutors have declined to move forward with ANY of the felony charges and the reckless speeding charge was downgraded to a misdemeanor.

And get this ... court records show Anderson was only ordered to pay a fine in the misdemeanor case (which he did) ... and it appears the case is essentially closed.

It's good news for Anderson -- but he could still be punished by the NFL if league officials find he violated the personal conduct policy.