The rude mom or dad that comes into a retail store looking for a Nintendo Wii during supply shortage only to discover they are out of stock and decides to argue with a manager or sales associate as to why they don't have any for sale. Wiihole is very similar to the use of asshole.
"Did you see that soccer mom over there trying to find a Wii? She argued with me for 10 minutes because the Wii was in the sales paper on Sunday and now we don't have any. Maybe if she came in and tried to buy one on Sunday instead of Friday, 5 days later she would have had better luck! That bitch was such a Wiihole...."
a wiihole is acting like an asshole while playing the wii.
being a wiihole is throwing friends off cliffs in super mario brothers, shooting them with shells in mariokart, or jumping around in front of your friend during their turn.