Aruch HaShulchan 167:31 and Be'er Hataiv 167:22 both say that it is forbidden to throw the (Challah) bread. I have heard that there are some people (I heard that there are some Rabannim who do so) that have a Minhag to throw the bread when passing it around Friday night. Is there a source for this Minhag? What is the reason? How does it circumvent the problem of throwing bread?
I was told orally that the Noda Bihudah, if I recall correctly, defends those who have such a practice as we seek to make our tables similar to the Mizbeach, and the meat that was to be placed on the fire on the Mizbeach (altar) in the Temple was thrown (past a gap between the ramp and Mizbeach).
A rabbi just explained that we throw challah at simchas to differentiate placing it in one's hand at funerals. We don't want to bring bad luck.
i have been told that the actual custom is to not pass it by hand but rather to place on the table or a tray for the others to take, and not necessarily to throw it. the reason being that the challah is zecher for the "mon" that was given directly by Hashem and therefore it (the challah) should not be taken from a person directly.