If you have to stop and think about whether it is a questionably frugal action or not, it is probably safe to not do it. For instance, recuperating the used salad dressing from the plates of your guests and pouring it back into the same salad bottles in front of their eyes is a definite social faux pas.
You can be fairly certain of never seeing those guests return to grace your doorway again nor the others in your circle who will certainly catch wind of this extreme escapade. Here's another frugal, more sanitary way you could economize on your salad dressing expenses: Put it in a smaller squeeze bottle and let your guests use the exact amount they want to.
Don't Talk About How Broke You Are
It's one thing to be broke and to let others know your budgetary constraints when they're trying to choose where you should all go to eat, but it's another thing to rub it into people's faces all the time.
At some point or another, you'll alienate your friends who will be sick and tired of hearing how you don't have two pennies to rub together. Your true friends won't even care that you're broke, but they certainly don't need to be awkwardly reminded about it each time you get together. They already know and are sensitive to the situation. If they forget, you can always politely bow out of the situation or suggest a more frugal option you could all do together instead. They'll get the hint.
Don't Be a Rainy Cloud on Others' Hard-Earned Sunshine
It's nice to offer ideas on how someone can save money by buying Product A instead of Product B because it's essentially the same or to tell them when the store's next predictable sale will happen so they can save some money. People love and welcome ways to save money on things and services. However, if you say he or she doesn't need Product A because he or she could make it out of scrap lying around the house for pennies or berate him or her for spending so much money on something so unnecessary, all you're doing is making the person feel guilty for not being broke. If you really feel strongly about it, try and find a nicer way to suggest a more frugal item or service.
Don't Be an Obnoxious Penny-Pincher
Yes, it is a virtue to be frugal, but there are times where an attitude that is too frugal can be quite impolite. For instance, if your colleague comes dressed as an elf and cheerily asks if you want to participate in the office's Secret Santa this year, don't refuse in a rude manner by saying: "Oh, the budget is $25 this year? I won't do it unless it's 20." Politely decline because it isn't in your budget this year.
The Bottom Line
The bottom line is that how people want to spend their hard earned money after they've saved for retirement is not really your concern. It's their disposable income, not yours, and although you may think you're helping or teaching them frugal behavior, you may just be raining on their parade and alienating them.