If you look at someone and see no reasonable probability you’ll ever have a positive or instructive interaction with them, block now and move on.

Ken White (b. c. 1969) American constitutional and criminal attorney, prosecutor, blogger
Twitter (2022-09-13)
    (Source)

Commonly known as "The Popehat Rule" (after White's Twitter account handle). An earlier version reads:

Block early, block often, block whenever you feel "I think I would enjoy not knowing this person.
[Twitter (2022-06-23)]

This should not be confused with Popehat's Rule of Goats or Law of Goats, e.g.:

He who fucks goats, either as part of a performance or to troll those he deems has overly delicate sensibilities, is simply a goatfucker.
[Urban Dictionary, "Popehat's Law of Goats"]

If you fuck goats because it upsets people you hate, you're still a goatfucker. Nobody cares that you're an insincere goatfucker.
[Twitter (2017-02-19)]

The Rule of Goats: even if you say you're only fucking goats ironically, you're still a goatfucker.
[Twitter (2017-04-30)]

If you kiss a goat, even if you say you’re doing it ironically, you’re still a goat-kisser.
["Is Alex Jones an extreme conspiracy theorist or a giant troll?" Los Angeles Times (2017-04-11) (Paraphrased "for this family newspaper")]