Anni... Glad you found these helpful.
Behnam... Your example of "cruel kindness" is a perfect example of a common oxymoron.... thank you.
The expression "tough love" is similar. It means that someone is being very strict with another person because they love them so much... like a father who is very strict with his children.
Muhammad... You are right, oxymorons are used in poetry and for emphasis. But they are also used by native English speakers as simple expressions.
Антон... Those are unusual expressions/phrases. They are not oxymorons, but they are funny... thanks