Mine would have to be Karlach when she is sneaking around she goes: "Shadow-lach" and then proceeds to be sneaky and dance walk while she sneaks. She is my favorite.
I always love when I've been off in some menu or something and close it to find her just dancing in the background for no reason. She's just so happy to be living her own life, it's precious
For me, the line that caught me off guard and had me laughing is when Astarian goes to bite your neck... 'Shit' the whole situation, the facial expression, the delivery. It lives rent free in my head since EA.
Grease mephitis in the sewers. This exchange pops in to my head at least once a day for some reason:
"What did the wizard say this river was called again?"
"I believe he called it 'the SYOO-ER'"
"Well what ever it is, it's impressive, and it tastes great"
Something about the cadence and delivery from the voice actors just make me laugh every time. Honestly, even for the most random of characters, all the voice actors absolutely killed it in this game.
The Goblin trader that gets left in the Goblin camp. The way he says "Praise The Absolute" whilst brushing his finger across his nose is so well delivered. Reminds me of a character from a Monty Python sequence.