In "The Gym", Elise's robot duplicate looks exactly like her, while the other robot duplicates look like enhanced versions of their human counterparts. Elise is already in excellent shape.
Considering who we find out runs the mafia, 'cupcake' being their codeword for 'kill' makes sense.
Part of why Dan couldn't hear Chris correctly in "Art"—hearing "naked Chris day" instead of "make it a Chris day"—might have something to do with the fact that Dan was driving at the time he called Chris. We even hear a car pass by on Dan's side of the call right when Chris says "make it a Chris day,"; it's subtle, but it would make it harder for Dan to hear Chris correctly In-Universe.
In "Vegetables," why do the burgers Dan passes out to people look so plain? There was only the buns, patty, and what looked like some ketchup. Dan doesn't like vegetables (and was protesting them in that episode anyway), and he can't have cheese or other dairy products; buying a bunch of burgers the way he likes them ensures that if he gets hungry he can just pick any random one to eat as opposed to checking each one for cheese.
In "Dancing," Chris mentions Elise's parents signed her up for a lot of activity-based classes like skeet shooting and martial arts. Given the fact that Elise Sr. is in the Mafia, it makes sense that Elise's mom would want her daughter to have all sorts of combat skills in case she ever joined the "family business".
Early in the series, we see Dan yelling at his grandmother on the phone as well as "some explicit letters made out to someone named 'Grandma'". Later in "Traffic", while Dan is stuck in traffic, he states out loud "Why did that funeral have to take so long!". Later in "The Beach", when Dan is thought to have been stranded and will die, he points up and shouts, "Well here I come, Grandma! You jerk!" Yes, the writers are even more evil than we thought. "The Gym" takes this one step further, the implication being that Dan may have actually had a hand in her death. Only after stealing her deviled egg recipe on her death bed.
The plot of "Burgerphile" involves Dan getting back at the Jerkass employee who refuses to admit he screwed up Dan's order. A Freeze-Frame Bonus however shows that the order was correct, Christ just took the wrong burger (He ordered one with cheese but was eating a plain hamburger). So Dan by the end of the episode accidentally ruined the career of someone who was completely in the right.
Since the cultists probably weren't all killed in "New Mexico", so they could have went back and continued the Human Sacrifice.
Also, probably a hand full of girls were killed in previous festivals.
The first part is unlikely as they were making a sacrifice for a good balloon festival. Since the balloons were destroyed, why would they continue the sacrifice?
Well they never actually completed the sacrifice. Maybe if they had Dan wouldn't have blown them up.
"Lemonade Stand Gang" has the eponymous gang of hooligans harrass Dan to the point where he is afraid to leave his apartment. While that is, itself, fairly scary, keep in mind most of Dan's diet appears to be fast food—his fridge is full of expired goods, and he eats out at Burgerphile enough that his glove box is completely filled with their receipts. With the gang harrassing Chris too, Dan's supply line was essentially cut off; without intervention, those kids could have starved Dan within his own home.
In "High School Reunion", Dan learns he has the approval of his former classmates (who he really seemed to hate until then). Are his complicated (and dangerous) revenge schemes merely the result of years of experience, or has Dan been going insane since high school and nobody noticed because they thought he was cool???
Why would Dan think his classmates he hate him? Dan said his adolescence was "[...] constant ridicule and that was just high school." implying that his home-life wasn't too good either. If you take it a step further, whatever it was, it caused him to be wary of people and assume the worst which in turn made him assume every minor thing his classmates did was a sign they were out to make his life a living hell. I mean, would it be any different than he acts now? Or since they loved his revenge schemes so much, they could have been intentionally provoking him for their own amusement.
In "Summer Camp", we learn that Dan's Start of Darkness occurred when he was still a prepubescent boy at the latest. And that's assuming that his widely hinted at Hilariously Abusive Childhood didn't have him screwed up since infancy.
The last time Dan saw his camp counselor, a child untrained in archery was trying to shoot an apple on the top of his head and it is implied that the child may have missed and killed the counselor.
Implied, nothing. Chris states that the Warriors regularly play "William Tell" with the smaller kids, and the camp "loses" one or two kids to the game every summer.
This episode could possibly be inspired by the Robber's Cave experiment, or the realistic conflict experiment. Specifically, the part of the experiment where the kids revolted against the instructors (The horrifying part is that the kids in the real experiment were signed up for it).
Actually Chris is a Yetiman so that could be part of it.
Chris's being a bear-man (and his earlier ability to ride a grizzly) are part of his latent Canadian-ness, which he only expresses when he's in Canada. They don't come up in "The Family Camping Trip" because that happens in the US.
If the average human can WALK 2mph, how come it takes everyone too long to jog/run a marathon in "The Cat Burglar"?
Elise Sr. claims Dan's deviled eggs "taste exactly like the ones [her] mother made, only for special occasions" and that she "took the recipe to her grave". Dan, of course, stole the recipe from his grandma on her deathbed. It could be possible Elise Sr. is Dan's aunt, making Elise his cousin.
Which actually explains his seemingly irrational hatred of her, having started as familial rivalry.