Just tell me you didn't melt when Dan found Mr. Mumbles...
Hell, Mr. Mumbles is a Crowning Character of Heartwarming. Dan's interactions with her are just adorable.
Dan letting Chris destroy Canada.
The entire tent scene with Elise, Dan, and Chris in Vs. George Washington. I never thought I'd say this about Dan but... awww.
Most of the scenes with Dan and Hortense. It's just so strange seeing Dan be so nice to another human being, even wooing her with Shakespeare quotes. Too bad it doesn't last...
It's quite notable that Dan never, at any point, takes any of his anger out on Hortense during that episode. He is completely in his right to complain, but he always treats her nicely because, well, she had nothing to do with the screwup and was willing to help out anyway. All of that was adorable.
Mr. Mumbles' birthday party. Dan got her a big mouse-shaped cake made of sardine and liver.
Hortense saying goodbye to Dan.
Dan's Not So Different revelation concerning the Dinosaur is oddly funny and heartwarming. He just can't stay angry at a fellow lazy, television watching, burger munching misanthrope.
Dan's bonding with little Dennis (in a twisted way).
The end of the fight in "Chris" shows that Dan does genuinely care about Chris (At the very least, enough to prevent him from falling to his death off a cliff).
Shown again in "The Boss". He's more willing to exorcise his demon boss rather than sacrifice Chris for his own personal gain. Considering who Dan is, this is saying a lot.
Chris getting absolutely furious over Amber taking advantage of Dan in "Anger Management".
The Reveal that Dan was beloved by his high school classmates.
Even though Dan dragged Chris along for their camping trip in front of the DMV and told Chris to be the lookout, Dan gave Chris a nice crossbow instead of keeping it for himself and his protection. Normally, this would not be a Crowning Moment of Heartwarming, but this is Dan we are talking about.
"Summer Camp" is one big giant heartwarming episode between Dan and Chris. It shows how they first met and became friends. It really goes a long way of showing why, in spite of all the crap Dan puts Chris through over the series, he is so important to him.
Dan refusing to leave Chris in the prison area, telling him "you're the best friend i've got!".
The ending where Chris feels upset at not being able to win an award to take home to his parents... and Dan makes him a "Best Sidekick Award."