It's when you say "suth" in honor of Kiefer Sutherland. It is most appropriately used after someone else moans or groans or says "oh/aw".

If you're really gay, you can drop a suth bomb after animals or inanimate objects make noise.

The best known way to retaliate against a suth bomb is by saying "kief" in response (a.k.a kief bomb).

When you eat dirt for the first time and leave your family to build a shack in the woods