When your fuckin a girl so hard that she starts bleeding, and you pull your dick out and make it wiggle like a red snake while "spitting your venom" on her face.

when you're hungover as shit after a spending a night drunk as a skunk

An extremely hard part on Through The Fire and Flames, which is contained in So Far Away III in Guitar Hero III. The Red Snake contains Star Power. On Expert, it's played as 32nd note Hammer Ons and Pull Offs at 200 Beats Per Minute, Clocking in at about 26.6 Notes Per Second.

When you have really bad diarrhea, to which burns while coming out and the "excrement" is brown/red colour.