The scene with Barnabs complaining about Willie writing his memoirs cracks me up too.
Another memorable scene between Willie and Barnabas occurs while Tom Jennings is preying on Julia. Barnabas frets about how her weakened condition will affect the experiment. "Is that all you're worried about?" Willie presses. He proceeds to egg Barnabas on, trying to get him to admit to his feelings for Julia, but the man is either too dense or too stubborn to pick up on the hints. Finally, exasperated, he demands, "Are you trying to be profound, Willie?" That particular interaction--the dramatic irony, the dialogue, and the nature of the characters struck me as being funny.
As has been mentioned, Roger's sarcasm could be very humorous. When parapsychologist Dr. Guthrie was called in to help a stricken Elizabeth, a dubious Roger suggested, "Why not do a voodoo dance around her hospital bed chanting semi-gutteral noises?"
Prof. Stokes could also be very witty and sarcastic. His first visit to Barnabas at the Old House, his showdowns with Angelique/Cassandra, and his semi-pompous, matter-of-fact reaction to the general weirdness at Collinwood always make me smile.
Carl Collins's practical jokes offered welcome comic relief.
Some scenes come across as humorous to me just because of the situation, the timing, and the presentation by the actors. I found the interactions between screw-up sidekick Aristede and Count Petofi to be funny, as well as some of the scenes between Bruno and Jeb. (e.g. "Don't worry--you've got Bruno!) Seeing anybody outwit Angelique or one of the Trasks makes me laugh. Even if these instances weren't written with the purpose of being humorous, the execution of the scenes or the poetic justice made them that way.
ProfStokes