You thought it'd never happen ... but Johnny Manziel is back making throws in an NFL stadium ... kinda ... playing parking lot pigskin with some fans at the Cowboys/Giants game Sunday night.

Manziel is still on a NYC trip that saw him take in the Heisman ceremony (he won that thing, remember?) and took some time to toss the football around with some fans before last night's game.

There was some talk before the season that Johnny might be the one taking snaps for the Cowboys INSIDE the stadium at some point in the future ... but yeah, that definitely ain't happening now.

He also tailgated in the FREEZING weather ... dude is a full-on superfan now.