Cell phone bombing

When you call someone and the only thing you say before hanging up is something you know will irritate them severely.

An example of cell phone bombing is calling up a friend who is deathly afraid of spiders and yelling "SPIDERS! SPIDERS, EVERYWHERE!!!" and promptly hanging up.

I cell phone bombed my brother, who is very OCD in his dislike for odd numbers, by calling, saying "I see sevens," and hanging up.