One of Mr Bean's quirks is that he hates this particular three-wheeled car:
My question is then, do we know why he hates this car? Has Atkinson or any of the writing staff ever commented regarding this hatred?
It's a meme.
In the UK, everybody hates those cars.
Google refs: Jeremy Clarkson/Top Gear, Reliant Robin or Reliant Supervan; Only Fools & Horses.
Try this Youtube video to see Clarkson "testing" one -
Even the members of the owner's club in the Top Gear video are quite aware of how bad their cherished vehicles really are.
Seriously, they were actually quite dangerous, unless you kept additional weight on the passenger side.
This is the "Supervan" variant, made [in]famous by Del-Boy & Rodney Trotter, in Only Fools & Horses.