Hmmm... that's an interesting complaint...never heard that one before.
I think they were referring to if you wear a lot of synthetic material (nylon, polyester, fleece, etc) they make an absurd amount of static charge when moved across other synthetics (like your seats)...I don't think they were trying to insult your choice of clothing...
Sounds like there almost could be some kind of strange reaction happening between the interior and exterior surfaces when the car is in motion or something that is causing a strong static charge that's not being discharged...for one thing I'd be careful to make sure you are neutralized before pumping fuel into it...touch the metal sides of the pump dispenser and your car door/body at the same time before pumping and don't get back in the car while it's fueling...
You might want to ask the dealer if the car has Electro-Static Discharge (ESD) protection for the interior and if there might be something wrong there...that much potential energy could be dangerous for fueling, could harm electronics, cause spontaneous airbag deploy, etc...
Maybe phrase it to them that way and see if it gets their attention...