GlowWorm
When a person places one or more glow sticks in their arse, often for sexual pleasure or drunken amusement, in the dark. Often used as part of dogging / voyeurism / public sex to help guide would be suitors / voyeurs.

Also known as a firefly or beacon.
example 1 : "Jill went dogging last night, and did a glowworm, after 10 minutes she apparently had a queue of suitors and countless people watching in the shadows! She said it really got her off!"

example 2 : "man we were so pissed last night, we found a bunch of glow sticks and did a naked glowworm race down the street - the loser had to buy the next round"