A light bulb with a large curly filament is connected alternately to 110 V AC and DC sources. A magnet is brought near the bulb. The filament under goes a steady deflection in the case of DC, but vibrates impressively in the case of AC.
The difference can be further illustrated by hooking a large inductance or capacitance in series with the bulb. The inductance "passes" DC but "blocks" AC, whereas the capacitance "blocks" DC but "passes" AC. See Capacitors and Inductors [1] for details.
Here is another demonstration of AC: A bicolor LED is connected directly to the 110V AC line. When the instructor swings the LED around her/his head, the light flashes green then red, showing that the LED is lit for only one half of the AC cycle. The same LED can be connected to a DC source, then the LED has one polarity, either red or green.
Links:
[1] https://demoweb.physics.ucla.edu/node/167