Q: How do I exit a bash when I'm party-hopping ?
A: Thank the host for the invitation, say you had a really great time and compliment them on a special aspect of the party, like the food or decor. Take the emphasis off your departure by making a tentative reference to the next time you'll see each other. Apologising has a negative impact, so just say you wish you could have stayed longer, but have to go. You might also want to offer to help clean up the next day. Chances are, they won't take you up on your offer, but it makes you look considerate.