n. An unwelcome erection which arrives at the most inconvenient times and is hard to get rid of.
E.g. Yo Tony blud, lessons over, lets split.
Tony: Shit! I can't stand up, I got Jehovah's stiffness init!
A Jehovah's Stiffness is a completely unwanted erection that appears at the worst of all times and once it appears, it absolutely refuses to go away for a VERY long time.
In reference to a Jehovah's Witness
For example getting a Jehovah's Stiffness on the bus or train just before your stop and you have to stand up and walk away but you know you can't is really annoying