If you happen to be thinking of one person while you are doing another, keep your verbiage to a minimum, in case you mistakenly call out the wrong name. If you inadvertently speak before you think, remain calm, carry on, pretend you didn’t even realize you spoke the misnomer, and pray to the gods above that your partner didn’t hear it.
If the gods are frowning upon you and your partner did hear a third missing party’s name, play “dumb,” but only if you can deliver a convincing performance. Either way, you must ultimately bend to your partner’s will with the utmost humility, explain it was simply a matter of misfiring synapses and a slip of the tongue, all the while figuratively (or literally, if they like) bestowing kisses to their posterior.
Should you be the recipient of such a dagger to the ear, it’s totally fine to be outraged and hurt. It’s also completely acceptable to put a halt to the rutting immediately. However, keep some perspective on the matter. It’s not like your partner actually cheated on you with this third party — though it is much more disturbing than if your lover had merely shared a platonic cup of coffee with said party. Behave accordingly.
For more on sexual etiquette, see our Sex Etiquette for Ladies and Gentlemen.