The person using, of course!
What happens is that all ascorbate devs (Xtol, Paterson FX-50) may die suddenly without any color change to indicate end of life, and all you get after dev is a blank film.
So, the nickname.
Both Patrick Gainer and Ryuji Suzuki are trying new formulations to avoid it.
On the other hand, there are people that have been using Xtol for years without any incident.
Water contamination by iron (rusty pipes, etc) is the most likely culprit.
See Ryuji's site (PhD student in chemistry, link I've posted above) for a short layman explanation.