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to joke; to jest; to kid; to josh
to make fun of; to laugh at; to play a prank
to romp; to gambol; to frolic; to frisk; to mess around; to fool around; to screw around
to neck; to make out
ふざけているのか本気なのか分からない。
I can't tell if you're joking or serious.
子供たちが教室でふざけて先生に怒られた。
The children fooled around in class and got scolded by the teacher.
彼とはふざけ合える仲の良い友達だ。
He's a good friend I can joke around with.