The Denver Broncos broke out the shears and went to town on the rookies -- shaving their heads into the best terrible haircuts ever ... and it's fantastic!!

It's a years-old tradition in Denver dating back to when Tim Tebow was drafted back in 2010 (remember, he got the "Friar Tuck" hairdo).

This time, it was Von Miller and Brandon Marshall as head stylists -- busting out everything from a checkerboard look to a MarioKart racetrack cut ... they even shaved a dude's eyebrow off!

Some of the victims ... Garett Bolles, De'Angelo Henderson and Brendan Langley.

It's all in good fun -- and it'll all grow back. But funny as hell.