A person who behaves in the manner the stereotypical dad would. This includes, but is not limited to, Hawaiian Shirts, dead memes, and the regular dad joke.
One need not be a dad to earn the title of "The Dadliest."
Paul: Guys, let's goget some food. I'm really hungry.
James: OH, NICE TO MEET YOU, REALLY HUNGRY! I'M JAMES! *dabs*
Tom: James, you truly are the dadliest of them all.
The act of cheating in a game and taunting your friends as you do it in order to piss off your friends so you can laugh at their expense. Popularized by many YouTubers, notably SeaNanners.
Person 1: "Hey, you can't get me up here."
Person 2: "Stop fucking cheatsy doodling!"
Person 1: laughing maniacally "CHEATSY DOODLES!!!"