a cuck chair is a lonesome chair, or one that stands out in such a way, usually facing the bed in a hotel room; a chair that a cuck could reasonably use.

a cuck is someone who enjoys watching their partner have sex with another person (usually called the bull) while not participating themselves, so they’d be sitting on that chair.

since these chairs are high up and overlooking the bed, the commenter is imagining two people/cucks sitting on these chairs like in a theater and commenting on the sexual performance. “it’s so hard” would be the first person’s comment about the erection of the bull’s genitals and “hard to watch” is the other person’s comment about the sexual act actually being unamusing or boring to watch. i assume these puppet characters speak in a similar way where they make wordplays and laugh about them together.