Why is my body the path of least resistance during a shock?
Electricity does not take the path of least resistance - it flows more through lower resistances and less through higher resistances. If you had a 10V battery feeding two parallel resistors and, the resistors were 10 ohms and 1000 ohms, 1 amp would flow through the 10 ohm resistor and 10mA would flow through the 1000 ohm resistor. It's called ohms law: -

Current = Voltage/Resistance or I = V/R

With mains voltages, current quite easily flows through the body and gets to ground via slightly conductive floors. Current can also flow due to body capacitance to ground due the mains voltage alternating at 50/60 Hz.

Because (usually) most AC supplies get grounded at the sub-station down the street, the return path is "guaranteed".