When GL is upset, he tends to yell insults at random strangers. We're working on it. When it happens, we remind him to use "appropriate words". When nothing but a bad word will do, we have taught him to "swear" using totally non-offensive interjections that we tell him are "bad words". Among his favorites: "bugs" "mud" and "dirt". As long as we act appropriately shocked, they seem to serve the purpose.