Pulled from the comments for Florio's article:
Brett Favre once played a prank on Aaron Rodgers before a practice session, asking him to autograph a helmet for a Favre 4ward Foundation charity recipient who specifically requested that Rodgers’ signature dominate the headgear.
Rodgers complied, but when he went to his locker to dress for practice his own helmet was missing. You guessed it–Rodgers’ helmet was the one that Favre had him sign, and he had no choice but to grab it and hurry out to the practice field to avoid being fined. (There was no “charity recipient.”)
Rodgers, of course, looked like a real prima donna as the only player at the public practice with his own gigantic autograph adorning his helmet. And Favre, for some reason, had a Cheshire grin on his face all afternoon.