Birthday Hater: With a twist; Bloo giving him surprise birthdays on almost any day except the actual day of his birthday (with one exception), he's grown something of a hatred towards them. It's mainly because he's put in embarrassing situations.
Break the Cutie: If Bloo is separated from him. Even if Bloo causes his most woobie-ish moments, he becomes an even bigger woobie.
Covert Pervert: Also, he was very curious of the "Adults Only" movies Frankie kept in her room. All the same it could be sort of excused, since it doesn't have to prove he's actually perverted; any child would be curious of what the adults are hiding from them.
Early Installment Weirdness: In season 1 episode "World Wide Wabbit", Mac is seen at one point eating cookies, but it's later revealed in season 2 that should he eat sugar, he becomes a crazy lunatic. Those cookies were maybe sugar-free, but still, makes you wonder...
Not So Above It All: Loads of times. Many episodes, particularly as the show went on, are built around him doing something more childish with Bloo and not being the voice of reason - or ironically applying his reason and wisdom to something immature.
Only Sane Man: This trope, however, is wonderfully averted if he eats too much sugar.
Mac: I don't like you! Not a person in this house likes you either! You're odd, talk in a weird way and really fast for that matter! Mr. Herriman is a rabbit, NOT a badger! Bloo's name isn't Chester, it's Bloo, bannanas don't contain protein you numbskull, nuts do! But you don't need anymore nuts since you're nuts! You're the place where they keep all the nuts! It's contagious! You spread the nuts to everyone in this house! Everybody thinks you're a nuisance and they all want you to just GO HOME!
My God, What Have I Done?: while Mac said that because he was so steamed, he looked in the present Goo was about to give him. Turns out she gave him a new backpack to replace the one that was rendered unusable at the start of the episode. Needless to say, Mac realized he shouldn't have snapped and apologized to Goo.
Out of Focus: Not in the show, but in the merchandise. Whenever merchandise of the series is released, expect Cheese to take his place (except for one shirt with both him and Cheese on it, and at least he did get a stuffed animal and figuriene of himself)
Ping Pong Naïveté: Rarely, but the show does still remind us that he's eight sometimes. For example, in "Camp Keep A Good Mac Down" he's his usual Wise Beyond Their Years self, basically being the only thing keeping the crumbling camping trip afloat - except for the scene where Eduardo tells him a scary story and he starts freaking out like a kid his age normally would.
Ship Tease: With Goo. He once held her hand to lead her out of Foster's, and she asked him slyly why he was doing that, which led many residents of Foster's to believe they were going steady, which he denies.
Vocal Evolution: His voice gets lower and somewhat scratchy after a while, due to his voice actor hitting puberty. This is very noticeable, especially when on the DVD Commentary for "Store Wars", you can hear him (the DVD came out during season five) talk against his higher voice in season one.
Open-Minded Parent: Both her parents are stated to be this (and possibly Hippie Parents too). Could be seen as a deconstruction too; her parents are implied to be way too open-minded, as they not only let her choose her own name as a baby (which is why she's named "Goo Goo Ga Ga") and allows her to dream up all those imaginary friends because they don't want to "stifle her creative mind", even though this terribly burdens Foster's Home and keeps her from actually making friends with the ones she's already made.
Ship Tease: With Goo. Mac once held her hand to lead her out of Foster's, and she asked him slyly why he was doing that, which led many residents of Foster's to believe they were going steady, which Mac denies.
Mac's mother, who made him get rid of Bloo in the first place, but is unaware of his daily visits to Foster's. She works all day, and Mac hardly ever gets to see her.
Adults Are Useless: Zigzagged. Mac's Mom is usually too busy to see Mac or deal with Terrance's bullying but unlike most cartoon moms, she's not oblivious to the abuse that Mac goes through, and tries to stop it. But to her, the problem is Bloo, and the series kicks off with her forcing Mac to get rid of Bloo. And the rest of series, she is completely unaware of the fact that Mac visits Bloo at Foster's everyday.
The latter is more to do with the fact that Mac's afraid of how she'll react than anything else.
Flanderization: He started out being very protective of Mac. Then he became a Jerk with a Heart of Gold in season one, more of a Jerkass in season two, and by the later seasons, some fans were wishing that Mac would just leave Bloo already.
The Friend Nobody Likes: Mac (his creator) genuinely likes him; at best the others tolerate him due to Proximity and Supervision.
Hidden Heart of Gold: When he thought that Eduardo had died he was devastated, and said nobody else deserved to be him. When Eduardo came back to Foster;s, he acted like he normally did, and said he didn't miss him at all. When everybody left, Bloo hugged Eduardo, and told him he missed him.
Dark and Troubled Past: While it's never stated in-universe, Word Of God says that Coco was created by a little girl that was stranded on a desert island. This explains Coco's bizarre appearance (body = plane, face = palm tree, lips/beak = deflated raft), her insanity, and her willingness to protect others.
Hidden Depths: Despite her weirdness, Coco seems to be the most resourceful and practical member of the clique, often coming up with the right solution in a pickle.
Murder Is the Best Solution: While we can't really be sure, there have been three instances when her suggestions against a problem involve something that Mac and Frankie said "would get them into jail" or "be illegal", respectively.
Gentle Giant: His owner, now a grown police officer, made him to not only have a playmate as well as protector from bullies, but to also have someone who was gentle enough to play with her baby brother.
Cowardly Lion: However, having a protector backfired. Instead of teasing her, the bullies started to attack Ed, who was too cowardly to defend himself, despite his looks.note She eventually got sick of it and lashed out the bullies in return, and began to protect Ed instead of vice versa. Ed's a natural cry-baby, and refuses to go into a suituation unless someone's beside him or he's in a group, and even then he's not going to be happy.
Well-Intentioned Extremist: Most of his strict rules revolve around not wasting resources (As it's a common plot that Fosters' budget is very tight) and simply trying to keep a semblance of order in a building filled with some rather wacky creations.
He has been shown to be a Reasonable Authority Figure at times, notably when Bloo accidentally knocked over a bust of Madame Foster and was terrified that Herriman would throw him out. Herriman instead calmly explained to him that he does not punish innocent mistakes, and that people have been knocking that bust over for years.