They Have The Power To Restrain You
You better behave yourself the next time you fly. If you get too unruly, then your flight attendant has the authority to arrest you (or at the very least, restrain you). You may have seen people removed from a flight before take off, but what happens when things come to light mid-flight?
If a flight attendant really needs to, they have the power to restrain overly aggressive or trouble causing passengers. They usually have zip ties available or they could use the seatbelt extensions as restraints. The passenger would then be placed in an area where they can’t be disruptive and would be escorted off at the first stop.