Mumoftwoinprimary
Sounds to me like they're one of those drivers who would like to park right in the middle of two spaces, but is too much of a coward to do so blatantly - so instead, they park right up to the line in the belief that they've subtly rendered the next space unusable.
When a doughty person such as yourself 'thwarts' them and does indeed manage to park there, in their eyes, you are the selfish baddie.
although it's Hugely annoying, you either need to scramble across from entry through the passenger door and over the gear stick or wait for their return
Out of interest, how would you feel if somebody blocked you in on your drive? Would you patiently wait for them to return then, or would you start thinking of ways that, although not deliberately damaging their car, may lead to incidental damage?
It may be that the person you've blocked in has just gone on a jolly jaunt for no reason and is also quite partial to an unexpected stroll around a supermarket car park; but how dare somebody decide that their time and daily schedule is far more important than yours, so that whilst they can get on with doing whatever they want/need to do, you are forced to drop whatever plans you had in order to hang around waiting for a stranger?
Also, what happens if it's a pay car park and waiting for them forces you to pay for another ticket to spend more time in the car park whilst you need to be getting on with other things and absolutely don't want to be there?
You simply don't have the right to deliberately control anybody else in this way, especially a stranger - who could have any number of truly urgent things that they need to do.
I would never wantonly bash my door against theirs in a rage (don't want to damage my door either), but if their forcing me to squeeze in (if at all possible) led to their car getting inadvertently damaged, I'd say that's 100% their own fault and no more than they deserve.