Griefing is a daily thing on almost every online game and will always exist, it is not exclusive to warcraft 2. There are many things you can do to combat griefing in some games, Discing is a form of both griefing and cheating though. Griefing in that you're wasting the other persons time by making them watch you on a drop screen for 45 seconds. and cheating in that they are removing their losses, and your wins from the ladder and in-game stats.
Regular griefing would be killing watchers, hiding units when losing rather then just leaving, playing a team game, building towers in your allies base under the impression you will protect them, then unallying them when they are all finished upgrading. Hilarious for the person doing it im sure, not so fun for the person on the receiving end.