Aaron Donald says if you're jumpin' off the Rams bandwagon after their ugly loss to the Bears ... you're gonna regret it -- 'cause the big DL tells TMZ Sports, "We'll bounce back!!!"
L.A. got punished in Chicago on Sunday night -- lookin' like a soft team afraid of the cold in a 15-6 loss -- and many are callin' the 12-2 Rams a fraud now.
But, when we got their superstar D-lineman at the Sports Illustrated Sportsperson Of The Year ceremony at The Beverly Hilton ... his message for L.