Leaving the party early when you’re done isn’t rude. It’s knowing your battery.

Social energy is finite and the amount varies enormously between people, which nobody announces, so everyone assumes their own level is the standard one. Staying past your limit does not buy you more of the evening. It buys a worse version of you, quieter and more irritable, while the good hours you already had get painted over. Leaving while you still like everybody is a better ending.

Decide before you go out roughly when you will head home, then go without making a speech about it. Thanks and a wave covers it. Nobody remembers who left early, only who was good company while there.