Getting the nixie supply across the heart with sweaty hands, it could kill you if you're particularly unlucky. There's the apocryphal tale of the guy that electrocuted himself with pointy meter probes on an old VOM (that uses 30V on some ohms ranges.)
If it's floating with regard to ground and you try to always keep one hand away from the supply while it's on, you probably won't even get a tingle.
If you do get a tingle off of it, consider it a lesson. Stop, turn things off and think about what you were doing before you do anything that stupid again.
Also, as a reminder, all your antistatic wrist bands, table mats, and floor mats should be at least 1M ohm to ground. Before you go messing around with high voltage, you might want to verify that.