"That's not nice!"

Translation: To není hezké!

[2200Lucia60]

To není hodné ! Is this also possible?

[VladaFu]

no, hodný is an adjective describing a person or an animal. Or an act (but not phrased like this). Alternatively, it can mean "hodný něčeho"="worthy of something" chvályhodný=praiseworthy.

Archaically, hodně (as an adverb) can also mean duly, properly. Rarely and archaically hodný can also mean due, proper but it certainly cannot be used here. I now survives in the nominal form "hoden".

[514dHoLL]

So "hezke" here can not be turned into other genders? Hezky(a) because is part of an expression, and is always the same? Why did it choose -e neuter? just a standard expression like "To je ono"?

[VladaFu]

To really requires a neuter adjective in the predicate.

You would need a noun for different genders. To není hezký kluk. To není hezká žena. To není hezké dítě.

If you are pointing at a male person, you can say: Ten není hezký. A female person: Ta není hezká.

But for some generic "it", you must use the neuter gender: To není hezké.

[AgnusOinas]

Just to add: you can even point at objects and you'll adjust the gender to match.

Pointing at a flower, "kytka" - feminine: Ta není hezká.

Pointing at a table, "stůl" - masculine: Ten není hezký.

Pointing at a car, "auto" - neuter: To není hezké.

Not pointing at anything defaults to the neuter-gendered "to".