A GFI is a Ground Fault Circuit breaker. since 1972, ALL "wet" (IOW, outdoor, such as a swimming pool, deck, or such and bathroom) installations were required to have them, in new installations OR when remodeling.
What they do, is to OPEN the circuit if there is a "fault" to the neutral or ground wire-- such as a defective appliance that would become dangerous and give one a shock, or a hair dryer tossed into a tub of water. In less than the blink of a eye, they will kill the power to the circuit, thus preventing electrocution of someone.
Nowdays, nearly ALL hair dryers, curling irons and other "wet use" appliances have a GFI built into the plug. you can identify these with the large plug that has a "reset" button on it. If one of these falls into a sink or tub, the power will be cut to the device immediately, and prevent the electrocution hazard.
In your case, perhaps if the breaker tripping is in the bathroom, maybe you have a GFI there. Otherwise, I suspect the hair dryer is wasted and presenting a short to the power source.
The hairdryer is brand new (and has the reset thing on the plug). I’ve unplugged it from the bathroom and plugged it into a powerstrip first, and then plugged that into a different part of the house. OH!!! We live in an apartment, 2nd floor. Could that have anything to do with anything? I’ve lived in some other old apartments and never encountered this problem before.
What say you, Dr. Jack? Can I be saved?