What would be good prank that won't cause a break-up?

My boyfriend sometimes pranks me (playful though) and I have no idea how to do a prank on him. I'm always the serious one in the relationship. This time I feel like being funny.

What would be a good prank to do on a boyfriend without causing a break-up? One that both of us can laugh. Any ideas?

What would be good prank that won't cause a break-up?
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