What do you think were Star Trek's top most cringe-worthy moments ... the things that just made you embarrassed for everyone who was unfortunate enough to be associated with them in any way?
DS9:Rivals: The law of probability is modified, as if it were a physical law that could be modified.
VOY:Tuvix (I especially like how Tuvix appears complete with a striped shirt...

)
TNG:Rascals (although I did think the young Ro Laren was awfully cute)
TNG:Unnatural Selection (A person's DNA doesn't change through their life in the way it's depicted)
TOS:Mudd's Women (magic colored gelatin even styles your hair!

)
TOS: Pretty much any time a computer speaks.
TOS: Any time Kirk verbally convinces a machine to self-destruct
TOS: Any time a female is introduced, and then there's a close-up of her against a pastel background, a musical note plays, and one or more men ogle her.
VOY: Threshold
TOS: Spock's Brain
TOS, Ent: Any time there's a Nazi-themed, Roman-themed, or Western-themed planet...