10 Worst Star Trek Hairstyles
10Janice Rand

Janice Rand (Grace Lee Whitney) is attractive, and so was the beehive in the 1960's. But on Yeoman Rand (depicted in TOS: "Miri") that hairstyle looks like kilograms of fake hair were spent on it, especially the strands that were elaborately braided to a basket.
9Pavel Chekov on his bad hair days

Pavel Chekov's first appearance in production order was in TOS: "Catspaw". Besides representing the Soviet Union, the character was meant to attract young people. He was given a hairstyle like the members of the pop band The Monkees to that end. But the wig that Walter Koenig wore in the first couple of episodes was just too obvious and was later abandoned as his hair had grown out.
8Kes in season 1

A bit like Walter Koenig as Pavel Chekov, Jennifer Lien as Kes too wore a too thick wig in season 1 of Voyager (depicted in VOY: "Phage"). Kes's hair in later appearances looks more natural.
7Dara in TNG: "Half a Life"

In TNG: "Half a Life", the Kaelon Dara (Michelle Forbes) comes aboard to persuade her father to commit ritual suicide according to their planet's traditions. Given the serious nature of the issue, the anvil on her head is, well, a bit distracting.
6T'Lani and Kellerun in DS9: "Armageddon Game"

The T'Lani and the Kellerun have a lot more in common than they would admit. Unfortunately their competing hair stylists couldn't settle the question whether a horn above the ear or a towering man bun is superior, which led to centuries of war.
5Michael Burnham in season 1/2

Sonequa Martin-Green as Michael Burnham can be seen with different hairstyles, which are usually attractive. Well, maybe except for the one where Lorca's Tribble seems to have found a new home on her head, such as in DIS: "Brother".
4Vaalians in TOS: "The Apple"

The whole make-up of the Vaal people from Gamma Trianguli VI in TOS: "The Apple" is silly, and so are their wigs of big white hair.
3Enarans in VOY: "Remember"

How can we tame our messy hair? With an old fishing net wrapped around it! So people can't tell any more which is uglier. The Enarans, men and women alike, have turned every day into a bad hair day.
2Jadzia Dax in DS9: "Past Tense II"

It may surprise to find Jadzia Dax of all characters on this list. But I think the haircut in DS9: "Past Tense II" is very unsexy, as is her whole androgynous styling in that episode. Mirror Jadzia, on the other hand, appears with a gorgeous short hairstyle, beginning in DS9: "Through the Looking Glass".
1The Kazon

The Kazon are the unsurprising winners of the award for the worst hairstyle in Star Trek. A typical Kazon such as Maje Jabin of the Ogla in VOY: "Caretaker" looks like a Klingon with a bird's nest on his head.
Addendum
Bad hairstyles that don't quite fit the theme: McCoy's beard in "Star Trek: The Motion Picture", Data's beard in TNG: "The Schizoid Man" and Boimler's attempt at a beard in LOW season 5.