In Targum Sheini on Megilas Esther it says, Haman told Achashveirosh about the Yidden
that they are different and have weird Minhagim. The Targum Sheini lists all the Minhagim
that Haman complained about. One of them is , on Shavuos they go on top of the Shul's
roof and throw down apples.