For starters, Beast Boy is horribly re-imagined in the show as mostly a lazy, annoying couch potato and is nearly intolerant to the concept of "responsibility".
Like the rest of the Titans, he barely receives any character development and repeats his mistakes over the course of the series.
He acts extremely immature most of the time.
He can be rather selfish at times, hating on the other Titans for having a better future just because it makes him look lame.
In “The Fourth Wall”, he even twerked in front of the audience, only in his underpants.
His voice is screechy and nasally. It also doesn't help that he screams most of the time. What also doesn't help is that his original voice actor, Greg Cipes, reprised his role as this character.
In "Smile Bones", and Cyborg forced the other Titans to wolf down their food like they do, to the point of almost starving them to death.
In "Let's Get Serious", he accuses Cyborg for drinking his juice and caused the two with Robin, Starfire and Raven to lash out at each other until the Titans Tower is destroyed and the team disbanded (which is never bought up because every episodes in this show do not have continuity except for episodic parts)
He once got all the Titans mixed up in a pyramid scheme that landed them in mass physical labor to pay off their boss. He also claimed it was all to buy Cyborg a present, even though Cyborg said he didn't need to and it being clear Beast Boy was just being greedy.
Hypocrisy: He claims to be a vegetarian, yet he's shown to be eating meat in some episodes.
He once mauled Aqualad to near death (while fighting over Raven no less), despite being a "hero".
It’s worse when you think that’s either his milk or his bodily fluids or even semen (aka cum). Since male cows cannot produce milk, this is highly possible...
His overuse of "dude", "bro", and "sick, yo" in season 2 and beyond can get old pretty quickly and will get you on your last nerve in every episode.
Not to mention after season 2, Beast Boy’s speech patterns changed entirely and it sounds like “gangster” or “hipster” slang, it’s a failed attempt to make him sound cool and it sounds annoying.
He was at his worst in "Gorilla" as he refuses to obey and tortures Robin for no reason at all because he was a gorilla.
He's also a liar as in the episode "Matched" he said that if Raven told him why she won't date him he'll get out but after she told him why she won't date him he is touched and wants to kiss her.
He has become a rather forced-to-be-disgusting Warner Bros./Cartoon Network version of Phil and Lil from Nickelodeon's Rugrats, as well as a more immature and annoying hybrid version of both SpongeBob SquarePants and Patrick Star. But unlike SpongeBob, Patrick, Phil and Lil, Beast Boy here is no better.
His redesign can appear as cute for some.
He got some redemption in Teen Titans Go! to the Movies.