During October of 2007, where Nickelodeon characters were shown dressed as various monsters during commercial breaks, Squidward was dressed as what appears to be the Phantom of the Opera.
Squidward can also be seen dressed in a Santa costume during a Happy Ha Ha Holidays commercial.
In "Good Ol' Whatshisname", after stealing What Zit Tooya's wallet, Squidward is sentenced to 10 years in jail, an unrealistically long time. However, it should be noted that Squidward also ran a stop light and resisted arrest.
Squidward was hinted at having suicidal thoughts during a few episodes.
Squidward often talks to himself because he has few friends.
In Spongebob vs. The Patty Gadget, he invented a Krabby Patty cooking machine, showing that he may have a hand for inventing.
Squidward often mentions the running length of one episode of the show (Eleven minutes), usually in subtle ways. A recognizable quote would be: "I'll give him eleven minutes." from the episode 'Nature Pants'
In the episode "Just One Bite" right after Squidward forcefully places down a gravestone, Spongebob askes him, "Are you sure?". Squidwards response is "Does this look unsure to you!?" and an unappealing and disturbing picture of Squidward comes up. This is used in many fads such as "youtube poop" and it is known as morbid squid or Skodward.
Like a real octopus, Squidward's pupils are rectangular.
He was considered to be the protagenist of Spongebob, not "The Yellow Buffoon" as Squidward would call him.