TMZ Sports has obtained a pic of the handwritten apology note Johnny Manziel sent to the guy he fought with before a wedding in Hawaii last week ... in which he admits he "should never have done that."
We broke the story ... multiple witnesses tell us Manziel punched the guy in the face Friday night at the rehearsal dinner at the Four Seasons on the Big Island.
The next day, the other guy in the fight got a visit from room service -- a champagne and orange juice delivery with a note that read:
"Truly apologize should have never done that. Know this won't make it better, but hope it starts the day off alright. Best, Johnny Manziel."
Sources tell us Manziel is adamant he did not instigate the fight -- but knows he shouldn't have engaged the other guy ... hence the apology.