When Geralt talks with the Fisher King. The man speaks only in grunts, but Geralt is completely calm and asks detailed questions. The best part is when every response is a "mhm" until the witcher asks if the villagers are getting along with the vodyanoi. The Fisher King's response? A long "oooooooo".
And then, the witcher provokes him to say a few words with an insult. The result? The man acts very mildly insulted and showcases the language of a classy British gentleman.
The Lady of the Lake asks Geralt for a compliment. His attempt at praising her wisdom and virtue is practically laughed off. An attempt to compare her eyes to starlight is found to be insulting. Geralt finally attempts "Your ass puts others to shame." She really likes that.
You know that annoying grandma who constanstly chases you out of Shani's house? After the party in Act II, you can talk to her, and she'll yell at you for having your way with Shani (if you did), and you can respond with "Die, hag!" And then she lets out a scream and drops dead. That's one hilarious way to kill off a character everyone hates.
The scene where Kalkstein mistakenly assumes that the potion for curing lycanthropy is being administered by a virgin (as it requires a virgin's tears... it's not: Carmen, a brothel madam is the client) is funny enough, where Geralt groans in exasperation and tells Kalkstein he needs to get out more. But then a fridge moment sinks in... Why didn't Kalkstein offer up his own tears? Think on that for a moment.