Flying dumpster glitch
From Halopedia, the Halo wiki
The easiest level to do this on is The Storm, at Checkpoint Alpha.
Two players should find an empty dumpster, tip it over, and walk into it. The two should then jump at the same time, jumping repeatedly to lift the dumpster into the air. If the two players are skilled enough, they can even steer their improvised aircraft and use it to attack the Scarab.