Lady of the Lake
After visiting the hermit (in the Fields) and learning about the Holy Grail, when you next talk to the Lady of the Lake (on Black Tern Island), you'll be able to tell her that you've had a "revelation" and wish to go on a mission. The Lady won't be happy to hear this. If you tell her that you were just joking, then she'll sleep with you. If you keep talking about your mission, then she'll knight you Sir Bonehead.

"Geralt, must I tell you my desire or can you divine it?"