Relatives, roommates, bosses, neighbors, love interests, lunch buddies -- as long as everyone avoids the topic of m-o-n-e-y, we'll all get along just fine.

Eventually, though, it's bound to come up. The waiter forgets to split the tab, or the cousin has a surefire investment opportunity (or unwieldy gambling debt) -- and then, well, things can get pretty awkward. Or, worse, relationships and finances can be jeopardized.

How to mind your money manners
For advice on how to graciously handle delicate financial interactions, I went to the foremost source on all things etiquette, The Emily Post Institute, which (politely, of course) referred me to the manners maven's great-great-granddaughter, Lizzie Post.

Two years ago, Lizzie penned a modern-manners guide for twentysomethings, called How Do You Work This Life Thing? Clearly, tact runs in the family, as does straightforward, commonsense advice: "One thing to remember with etiquette is that you almost never have to bite your lip and feel forced into doing something you're uncomfortable with -- financially or otherwise."

The key to dealing with awkward money moments is to prepare for them. "A lot of etiquette is about prevention," she says. "It is much more about making your life realistic and not being a pushover or a doormat for people."

Here are her top tips for preparing for a host of uncomfortable money-related interactions:

Splitting the check
How to enjoy a night on the town when you're on a salad-and-tap-water budget and everyone else orders steak and merlot.

Lizzie Post: The best way to handle this is to head the whole thing off immediately by saying, "Tonight I really just feel like getting a salad. Let's do separate checks so it is easier on the waitress." If the check comes and it looks like everyone's going to split the bill evenly, that's your cue to say, "Hey guys, you know what? I only ordered a salad, so here's what will cover my meal and tax and tip." That way they know that you have covered all the bases and aren't trying to skip out on your fair share.

Picking up the tab
To treat or not to treat? The answer is in the phrasing.

Post: If your boss says, "Hey, Katherine, do you want to come to Blimpie's and grab a sandwich?" that is a casual ask. If he says, "Let's go to lunch to discuss work," that's a more formal ask, and he should pay for the lunch. If you're unsure of the intention behind the outing (like is it a date or are we going out just as friends?), you could say, "Sure, but could we stop at an ATM so I can get cash?" That gives the other person the opportunity to say, "Oh, no, I will cover it," or "Sure, no problem."

Suffering from many parties and too few paychecks
When suffering from obligation overload, it's perfectly OK to just say no -- at the office and even to your best friend.

Post: Prioritize. Choose the things that you need to be a part of and those that are really important to you. If, for instance, you are asked to be a bridesmaid or maid of honor and you are on a tight budget, tell the bride what you can afford to commit financially and let her know that you understand if she might want someone else to do it. Tell her that you'll be with her in spirit no matter what. Maybe that means that you skip her engagement party but you attend the bridal shower.

At the start of the year, decide how much you are able to contribute to things like office party birthday pools, charity drives, and Girl Scout cookie sales. That way you can say, "I am really sorry, but I have contributed what I can on donations this month." Or ask your company to set up a panhandling policy. Fliers above the watercooler can alert those who want to contribute and take the pressure off you. The bottom line is you have got to be responsible. It is OK to say no.

Handling handout requests
Four to-dos that will help you avoid feeling like a human ATM.

Post: First, if you're being asked for a loan, think of it as a gift. Can you afford to give this person money, and can you afford to never see the cash again? Second, can you afford to risk the friendship over this money? The third thing is whether or not you are comfortable -- both financially and with giving it to the person asking. If you are not, say no. Finally, create a written agreement, no matter whether it's with your mother, your daughter, your best friend, or your husband. Write down the amount that is being lent and what the agreement is to get it paid back on time. I highly doubt that legally it could help you in any way, but it helps avoid any misunderstandings.

Dealing with the rich friend-poor friend disparity
Stop salary disparity from putting your relationships on uneven footing.

Post: Often I find that the person who doesn't make as much feels guiltier about not pitching in. But after a while when one person is always picking up the tab, both may get too accustomed to the arrangement. If it is getting under your skin, no matter which side you are on, you need to have a conversation. Focus on the fact that your enjoyment comes from your time together, not the amount of money spent. Explain that you understand his financial situation but that it would make you more comfortable if the relationship were a bit more even right now.

Giving and receiving -- the unexpected gift
Are you now expected to exchange gifts with this person for eternity?

Post: A gift is a gift. It is a nice gesture. It is not something that has a forced reciprocation with it. The first and most important thing to do is enthusiastically thank the person for the gift. To just turn around and pull the, "Oh, oh, oh, I will get you something or I have something for you; I will bring it in tomorrow" actually takes down a notch the other person's gesture. We get so worried about making it up to someone else or leveling out the playing field that we forget that gifts are gifts for a reason. Then, you've got a choice to make -- you can get the person a gift or not. It's fine to thank the person and leave it at that. If you decide to give a gift, you'll likely establish a gift-giving tradition with this person, and you may not want to go that route. If you want to get them something in return, simply go get them the gift and give it to them at a different time.

For more Foolishness:

Ms. Dayana Yochim knows how to pass the salt and pepper (together), hail a cab while wearing heels, and properly set a table (with all the knives facing the right way, even!). The Fool's disclosure policy is always served with a cloth napkin.