Are these sentences OK?
I pray it never happens again.
İf you're not perfect, don't judge others.
Nothing can warrant such a behaviour.
Nothing can warrant such rudeness

Question

Answer

Everything is fine, except don't use "a" in front of "behaviour."  Also, as you probably know, the American English spelling is "behavior."

Answer

I pray it never happens again.
If you're not perfect, don't judge others.
Nothing can warrant such behavior. (behavior is uncountable)
Nothing can warrant such rudeness. 
** "Warrant" works well here, you can also substitute it for "justify"