kawaiko: I'd say record the situation they bully because they think there is no power over them or they are the authority record them from a distance and trust me they'll get mad but that'll cause them to fear the real authority your gonna report to and show it to its like ripping a mask of a criminal
Bullies love a reaction and a sense of power. Ignore them like they don't even exist. Have a "yeah, whatever" attitude. If it looks like you don't care, it makes you look stronger than them, because it seems you have more important things to deal with than waste your time with them.
call the Police
Set fire to them.
Hmm! Fight them!
Buy a gun