What can you say instead of nastiness?

It depends on the context of "nastiness" and what you're trying to convey. Here are some options based on different meanings of "nastiness":

If you mean rude or unpleasant behavior:

* Unkind

* Discourteous

* Inconsiderate

* Offensive

* Mean-spirited

* Unpleasant

* Rude

* Insensitive

* Unwelcoming

* Unfriendly

* Hostile

If you mean something physically unpleasant:

* Disgusting

* Repulsive

* Unhygienic

* Filthy

* Unpalatable

* Gross

If you mean something morally wrong:

* Evil

* Vicious

* Cruel

* Malevolent

* Wicked

* Devious

If you mean something that is unpleasant to look at or hear:

* Ugly

* Unsightly

* Unharmonious

* Cacophonous

More neutral options:

* Unfortunate

* Regrettable

* Inappropriate

* Uncalled for

* Undesirable

It's always a good idea to be specific and clear when you are trying to describe something as "nasty". The best option will depend on the particular situation.