A legendary permanent that is put into a graveyard because of the “legend rule” isn't sacrificed.

Havoc Jester's ability is a triggered ability, not an activated ability. It doesn't allow you to sacrifice a permanent whenever you want; rather, you need some other way of sacrificing permanents.

If you sacrifice a permanent as part of casting a spell or activating an ability, Havoc Jester's ability will resolve before that spell or ability.

Havoc Jester's ability triggers when you sacrifice it. If you sacrifice other permanents at the same time, it triggers for them as well.