Redwall/Funny

In the first novel, when old Methuselah discovers the connection between I - Am That Is and Matthias' name, he starts giggling and wise-cracking, causing Matthias to think that the grinning old guy next to him has finally snapped. Jacques kindly described it as "second infancy". And Matthias keeps thinking that for almost a page.
In Mattimeo:

"Mangiz does not forget an insult, hedgepig."
"Good, then here's a few more to remember, you brainless featherbottomed excuse for a duck."

[...]

"I will not stand here and be insulted!"

"Then stand somewhere else and I'll insult you there, featherbag!"

The Long Patrol: "If brains wuz bread, youda starved to death afore you was born!"
The Duel of Insults in Marlfox.
In Redwall, Basil's banter with Cluny while he and Jess were taking back the tapestry.

Cluny: "Get him! I want his head!!"
Basil: "What's the matter? Isn't your own head good enough?"

In Outcast, Balefur's entire introduction scene.

Swartt: "I am Swartt Sixclaw, leader of this horde!"
Balefur: "Aye, so you are. What else is new, ferret?"

- "Ferret smashed inta bits! 'Ead one place, paws another, tail inna nundred bits. Smashed ferret! Yeeheehee!"
- "Some warlord you are. I've seen more action from a squashed frog!"
- Jodd's full name.
Flinky and company in Loamhedge.
- At least before they kill poor Junty the Cellarhog. Luckily Laser-Guided Karma catches up to them.
The Running Gag about the mole who has a taste for wild garlic in Mariel of Redwall.
In Pearls of Lutra, paraphrased:

Tansy: "Put a paw near that frosting, and I'll smack it with this spoon!"
Clecky: *scoops some into his mouth with his ear*

In Long Patrol having just captured the painted ones the Hares shout out recipes for cooking him. When other others ask for some Rockjaw Grang responds that he's been doing all the carrying so this one is his so get your own he's going in a hotpot. After Major Perigord remakes that they are not really going to eat the rat Rockjaw simply says, "spoilsport"