You can only defend your trademark with respect to product categories that you actually market. Unless IKEA were in the business of selling parody video games, their trademark doesn't apply.
Wait... is that why IKEA just put out a parody video game?
You can also defend it against tarnishment. They can argue that IKEA appearing in a violent video game has negative associations with their trademarks.
The game featured a store and stuff in it, that's a product category IKEA markets.
If the name of an unrelated game was IKEA as some clever acronym or such and it was unrelated to stores, that would be a different trademark convo.