In rare form phrase
Doing or performing something extremely well
Holly was in rare form during her speech, so she got the first prize in the competition last night.
The actor was in rare form. His performance was recognized by the audience.
Behaving in an extreme or remarkable manner
Corrine: I'm going to buy Christmas presents for everybody. Do you want to go with me? Laura: Oh...My kids are in rare form today, so I cannot go with you. Sorry!
Josh is in rare form today, he tries to pick a quarrel with me.
People tend to like forbidden or illegal things just because they are forbidden or illegal.
He must have believed that stolen fruit is the sweetest, and he, therefore, cheated on his partner.