How to say “Don’t be mean” in Japanese?

意地悪しないで / いじわるしないで (iziwarusinaide)

1) あなたと違うからといって、人に意地悪してet はいけない / あなたとちがうからといって、ひとにいじわるしてはいけない (anatatotigau karatoitte hitoni iziwarusitewa ikenai)

Don’t be mean to people just because they are different to you.

tigau = different
kara (dakara) = because
hito = people
iziwaru = mean

NOTE:

Here are some “being mean” samples in Japan;

Total silence treatment – pretend the target person does not exist on earth and ignore anything and everything the person does.

Hiding someone’s possession- The item is probably not going to come back to the person who posses it

Eating someone’s lunch – the target will starve for the rest of the day

Spill water on desk – very wet desk surface sometimes along with wet bad and gym clothes

Fake rumors – it hits you physiologically