Using this tern will set you apart in slang use in DF. Originally it was used among rural people to refer to the venom of poisonous reptiles, and among elder people to refer to substances that have noxious effects (both correct). This term has been re-introduced to the urban vocabulary with an extended meaning, probably from the interaction of those rural new comers with the rest of the DF folklore.
This extended meaning is sexual. It refers to the male reproductive fluid, yes, semen. The usage is among guy talk but pretty straightforward. Like in any albur (double entendre) you want to give it away but not be recipient of it: venom is not good for your health. Here are some examples:
1. Andas ponzoñoso ca! (Dude, chill your horniness!)
2. Aguas! Ahí te va la ponzoña (Be careful, here I come)
3. Bájale a tu ponzoña (Fuck off!)
Part of the beauty of this word is in its phonetics, although not quite onomatopoeic it still reminds discharge. Be creative when using it. For example, elongate the middle syllable, pon- zooooo-ña, or give more intensity by stressing the nasal part, pon-so-Ña.