Anakin and Obi-Wan take time out from the opening battle to comment on R2's performance. For about five seconds they sound like his parents, with Anakin being the protective one and Obi-Wan asking why he's always the bad guy.
Obi-Wan: Well, R2 has been -
Anakin: Ehh, no loose wire jokes.
Obi-Wan: Did I say anything?
Anakin: He's trying.
Obi-Wan:(defensively) I didn't say anything!
When Obi-Wan regains consciousness while Anakin is carrying both him and the Chancellor, while hanging for dear life in an elevator shaft.
When Anakin and Obi-Wan argue about how many times the young apprentice had saved his master.
Anakin: You owe me one, and for not saving your skin for the tenth time.
Obi-Wan: Ninth time. That business on Cato Neimodia doesn't... doesn't count.
Made even funnier in the novel Labyrinth of Evil, when we see just what that "Business" was. Obi-Wan unintentionally got high and Anakin helped him finish off a group of battle droids that were attacking him.
Virtually all the snark from the droids at the beginning of the film.
When General Grievous snatches two lightsabers out of a poor downed Battle Droid's hands.
Battle Droid: You're welcome.
You practically feel the snark from that one. It passes by Obi-Wan and Anakin as it gives their lightsabers to Grievous and even says 'Excuse me.'
The scene where Anakin heckles Grievous.
General Grievous: Anakin Skywalker. I expected someone with your reputation to be a little... older. Anakin: General Grievous... you're shorter than I expected. General Grievous: Jedi scum! Obi-Wan: He has a job to do, Anakin. Try not to upset him.
Obi-Wan's total lack of reaction to everything going to hell during the battle of Coruscant.
"Not to worry, we are still flying half a ship."
For that matter, the entire Coming In Hot scenario with increasingly large portions of the ship bursting into flames and/or falling off as Anakin brings them in for a forced landing. What should be a terrifyingly catastrophic scene (all of those chunks of the ship are falling over a very large city, and the ship itself takes out several buildings at the spaceport when it ditches) ends up being hysterically funny, thanks to Anakin and Obi-Wan's deadpan commentary.
From the novelisation: Obi-Wan and Yoda are considering how they will get back to Coruscant post-Order 66, and look dubiously at the small one seater spaceship Obi-Wan arrived in.
Obi-Wan: I suppose... if you don't mind riding on my lap...
The novelization has a number of darkly funny moments whenever Grievous is forced to put up with Nute Gunray. Most notably: "Grievous resisted his natural inclination, which was to boot the Viceroy so high he'd burn up on reentry."
Another moment in the novelization. General Grevious subscribes to the school of You Have Failed Me management, and he has an even smaller tolerance for failure than Darth Vader. Reality Ensues with he gets fed up with one last panicking crew member... and then realizes he just killed the last of his bridge crew.