Getting off scot-free requires nothing more than a little bit of charm -- and these quick responses (according to Emily Post).

If you're double-booked...

call the host and explain your situation -- just keep it brief.

If you don't want to go alone but didn't get a plus one...

decline the invitation -- but be clear about your reason, since the host may decide to extend the invitation to your guest (or not).

If you'd rather stay at home and do just about anything else...

reply promptly, within a day or two; otherwise you'll seem like you were waiting to see if something better came along.

-- The Nest Editors