A carefully planned party can fall apart when an unexpected guest shows up. While it's extremely rude for an invited guest to bring a friend without first checking in, it does happen. You could choose to flex your host muscles and stand firm, but most etiquette experts recommend you step back and make the best of it, since the goal is for everyone to have a good time.
Handle the Situation Before the Party
Head off trouble before it even appears by communicating clearly with the invited guests. When they respond to your RSVP, you can give them the details of the event. For example, you could say that you're looking forward to just the twelve of you getting together. You could also pleasantly joke with them that they'd better not surprise you with uninvited guests. By gently and clearly communicating that it's not OK to bring a guest, you stand the best chance of getting what you want.
If an invited guest mentions that they'd like to bring someone when they RSVP, you'll have to decide how to proceed. If it's a casual potluck-style event or a cocktail party, it's usually no big deal to add another. However, if it's a dinner party or other structured event, even one more person might throw things off.
Dealing With the Problem at a Party
The party's in full swing and one of your invited guests has just arrived with a friend who was not on the guest list. The only course of action now is to kick into full host mode and make them feel welcome. Ask the invited guest to introduce their friend while you fix a drink for the unexpected guest.
The unexpected guest will likely not know anyone at the party, so do what you can to include them in the conversations. For example, you could mention that you've just read a wonderful book, and then ask the new arrival about their favorite author. Finding common ground between invited guests and an uninvited one is key to making the evening comfortable for all.
As the host, you'll be circulating among your guests, so it's easy to slip into the kitchen and do what you can to make room. Whether that's setting another place at the table, slicing another piece of cake or redistributing food portions, having a little time alone in the kitchen can smooth over an awkward lack of notice.
If you are having a dinner party with served portions, you'll have to compromise. Most etiquette experts suggest splitting the portion between the unexpected guest and the person who brought them.
True hosts may be tempted to sacrifice their own portion for the sake of the unexpected guest, but there's no reason that you should suffer when it's perfectly acceptable for the others to divide the meal. Sometimes there are just consequences for being an uninvited guest, and they may just have to go without guest favors, bottle of wine or other portioned item. Simply state that, while you are delighted that they came, you were planning on a certain number of guests. If you are honest, everyone involved will know you have done your best.
When to Say No
Sometimes it is appropriate for a host to say no. While the rule of thumb is to try to accommodate a single person, finding the food, space and time to handle more than one can be an unfair burden.
If someone brings several other people to your party, you are within your rights to say that you simply cannot accommodate them. Especially if it's a dinner party or a wine and cheese party and there will not be enough food, the host can decline to serve all of them. One solution is to seat the uninvited guests in another room with drinks, appetizers and music while the dinner guests are eating. Then share dessert with everyone by serving up smaller portions of the sweet stuff.
The other instance where it's appropriate to say no is when there might be awkwardness between them and one of your guests. For example, bringing in ex-spouses, ex-boyfriends, ex-girlfriends or those who have suffered a serious falling out could create a difficult situation. You are within your rights to tell the uninvited guest that it will be uncomfortable to have them stay for the party because you've invited so-and-so, and you'll have to enjoy their company another time.
Confront the Offender
Later, after the party, make sure you politely and privately confront the offender who brought the uninvited guest. State that while you enjoyed getting to know so-and-so, you found it incredibly stressful to have to accommodate an extra person with no notice. As long as they understand that their actions were not acceptable, you've gotten the message across.
The uninvited guest can often intrude upon your planned evening of quiet time, a family celebration, or a romantic dinner that was booked months ago. Or, you're at a group event where drinks and dessert are served and a party of six shows up although they turned down the invitation a few weeks prior.
When the phone rings, announcing that I have uninvited guests on their way to my very messy home, I realize that I need to clean up immediately. Fifteen minutes to prepare for a visitor isn't long, but it can be done.