I don't think anyone should be putting their bags in an overhead that isn't over 'their' head..it's rude to put a bag in the bin at the front of the plane if you aren't seated there.
Agreed! And if the space is intended to accommodate bags of the two or three people seated under that space, those guests have every right to reposition bags so theirs will fit as intended. The "gentleman" as described by the OP was totally in the wrong IMHO, for what that's worth. If the FA steps up to the plate an enforces rules or guidelines or reasonable expectations, all the better. But the guest sitting under that space should not be inconvenience by the arrogant space-hogging oaf.