The basic premise of Space Dandy isn't sexist by itself. An evaluation that attempts to determine if something is sexist needs to examine the camera angles, script, and art design in order to formulate an informed opinion. The problem with judging the entire series of Space Dandy is that a different person is in charge of each episode. It's not unusual for an anime to have multiple directors, but Space Dandy is special case because of the amount of freedom it allows.
Eunyoung Choi, best known for Tatami Galaxy, was the Director of episode 9(plant planet). She was also credited with credited with Storyboard, Art design, Guest Character Design, Key Animation, and Story Drafting. She, like all the other directors, was given complete creative control over her one episode. She brought in her own style and direction for this singular episode. Judging Space Dandy as a whole ignores that this is very much an artistic vision project.
I do think certain episodes indulge the viewer in a sexist way.
Take episode 2 for instance. There's a close-up shot of Scarlet uncrossing and crossing her legs. Dandy can't see her legs from that angle and Scarlet isn't trying to act flirty. The shot only exists to titillate the viewers. Yeah, I would consider that shot to be sexist. Personally I'm not bothered by it since the director is Sayo Yamamoto. I take it to be more like showboating. She is breaking the fourth wall to draw attention to how awesome her character is.
