As shown in, Dan vs. Dan and Dan vs. Burgerphile, Dan is lactose-intolerant. Eating cheese or milk based products makes him roll around on the floor clenching his stomach in pain.
In Dan vs. Baseball. Dan mentions he's been hit with tear gas so many times it doesn't affect him anymore.
Mr. Mumbles is a girl cat and he acknowledges it as a girl. He named her before he knew her gender, and didn't find out she was a girl until several episodes after he adopted her, but still calls her Mr. Mumbles anyway.
In Dan Vs. Elise's Parents, Don reveals that Dan was Chris's best man in Chris and Elise's wedding by saying, "I remember his best man speech where he tells us that marriage is a big scam."
It is shown that Dan does not like to be called angry, it's shown that in Dan vs. Dan and Dan vs. Technology, that whenever someone calls him angry, he starts yelling "Who's angry!?" and he puts his hands into a strangling motion.
In Dan vs Alien Elise Sr Told Dan not to Tell anyone about the Alien Invasion but he Told Chris about It.
In Dan vs Monster under the Bed Dan yelled out chris at the Ending. Then Dan yelled out Chris in Dan vs Chris