When people short hop fast fall constantly in neutral, you should think of it like dash dancing in melee or proximity blocking in Street fighter. They're moving in and out of your space trying to bait you into doing something punishable. When people SHFF they're trying to get you to enter within range of their attack, and then retaliate with an aerial of his or her choice. What aerial you retaliate with out of short hop depends on the start up, landing lag, range, and power of your aerials. For example,
may want to SHFF his Nair,
would prefer her fair, while
may prefer his Bair.
if you want to do this with Pit, I suggest you use fair due to its range and low landing lag.
If you want to see this in action watch some of Ranai's sets, and pay attention to when he short hops, you should notice how whenever the opponent attempts to move in he pops them with a sling shot. (He's a
main, in case you don't know)