get nasty
turn nasty BrE

"Is there any chance that these things could end up being used as weapons if the System turned nasty?"

I get a lot of attention from men, but when I've said no to relationships - sometimes they turn nasty.

It is also an issue that could turn nasty for Republicans.

And if the weather does turn nasty there's always a low level alternative.

Having been told that there was no chance of getting in, the crowd had turned nasty.

Some of them clearly had burned out and turned nasty.

Since the birth of her baby brother she had turned really nasty.

Suddenly it had all gone off and turned very nasty.

Yet when nothing happened, they didn't turn nasty, as you'd expect.

In a few days it would turn really nasty down there.