Funny / Sonic Underground
Episode 5 has this:
Sleet: Why are we stopped for a puny tree!?!
Sleet: [ suddenly nonchalant] Ah. That's why.
When Sonic calls the Oracle of Delphius out on his constant riddling speech, the Oracle has the perfect response:
Sonic: Don't you ever just give a straight answer?
Oracle: What do you think?
After stealing a supposed "ancient artifact" that Robotnik was trying to sell at auction, Sonic and Sonia take it to an antiques expert:
Expert: This artifact is not from Mobu Pinchu. It's only about 500 years old. It's from the last Mobian War— or at least, uh, the last one 'til Robotnik came along.
Sonic: Wouldn't Buttnik's own experts tell him it's not from Mobu Pinchu?
Expert: If Robotnik asks you a question, would you give him an answer he doesn't wanna hear?
Sonic: ...he's got a point there.
Sonic goofing off by playing tennis with himself ( and serving as the referee) in "Last Resort". Eventually he throws a John McEnroe-esque tantrum at one of his own decisions and storms off.
Sonic: I hate it when I'm a sore loser.
From "The Price of Freedom":
] Robotnik Intelligence Agent N, and you are hereby arrested for crimes against the state, and because... Dr. Robotnik
From episode 1.
Oracle: Come, Sonic! Your destiny awaits!
Sonic: Tell it to wait outside, I'm too tired to care.
The hedgehogs using the Do-Bot to erase Robotnik's memory of the cassette tape.
In "Wedding Bell Blues," there's this exchange.
Robotnik: Sleet, you idiot!
Sleet: No, sire. I'm the conniving one! Dingo's the idiot!
"Beginnings" has this exchange as Robotnik tries to figure out what the Resistance's secret weapon is.
Robot: Sensors indicate that the subject is... blue, sir.
Robotnik: Blue? Is that all!?
"Getting to Know You" has this.
Dingo: (on Sonia) She's pretty.
Sleet: And you're ugly. Now let's get to work.
Sonic and Manic disguised as belly dancers in "Who Do You Think You Are?".
Knuckles' memetic line from "Friend or Foe?"-
Knuckles: [ yelling] I
HATE THIEVES! Don't forget the exchange Sonic and Sonia had around the same time.
Sonic: I'LL handle this!
The Mirror Universe episode is a goldmine of laughs with the sheer incongruity of Robotnik as a freedom fighter, but perhaps the kicker is the moment when, after Mirror!Robotnik and the hedgehogs complete their plan to go after the Mirror!Hedgehogs, Sonic instinctively calls his new ally by the Ro-Butt-nik nickname. The hurt on Mirror!Robotnik's face and his startled Big "WHAT?!" are hilarious, as is Sonic's genuine contrition as he apologizes for it.