It's the best rookie hazing tradition in football -- the Denver Broncos line up the rookies, break out the clippers and go to work ... churning out the UGLIEST hairdos they can think of.

No one is spared -- including Chubb (the 5th overall pick in the draft) ... with every rookie looking like they just got buzzed up by Stevie Wonder.

Linebacker Brandon Marshall documented the damage -- some players got a checkerboard do ... others got a Coolio look. One dude got the ol' Friar Tuck (just like the one Tim Tebow got back in the day).

Don't worry ... it'll grow back.