Level 1 of Poison is 10%, +5% per level. I don't remember exactly whether it's max lvl 4 or 6, but still, it's basically 1 out of 3 or 1 out of 4 chance to poison when max (and PvP Tias tend to max since it deals 15+ damage per second for 15 seconds once poisoned). Being hit by ANY physical attack can potentially cost you 225 life in addition to whatever the attack damage was. It might be useful in team PvP, but unless the Tia's partner is also being juggled/inexperienced, they won't let you get off that Antidote without being punished.
"If someone asks you whether or not you're ticklish, it doesn't matter what you say, they're gonna touch you. If you don't wanna be touched, you gotta say something like, 'I have diarrhea. And yes, I'm very ticklish.'"