Although Emily Post may not have covered this subject in her best-selling book, Etiquette, there are some good tidbits of advice for ladies regarding flask use. Some women might carry one in their purse or pocket book, while others might be wearing an outfit where they can conceal the flasks elsewhere. These days, there are many small, cute, ladylike flasks available, and there’s no reason why a woman cannot carry one, with her favorite potable inside.
If she is to take a sip, in the presence of other females, she would be within the limits of good manners to offer a sip to the other girls first, before taking a sip of her own. If there are several women and one man present, she could offer any of the females a sip, by saying something like “Would any of you ladies care for some?” Once any of them takes a sip, she can have a drink herself, and then offer the flask to the man in the group. If there are a few men, they would be asked, after the hostess has her sip, “Would any of you gentlemen care for some?”
Another bit of etiquette [for both women AND men] would be to make sure not to gulp, drink too fast or noisily, and certainly hold back any consequential belch or vocal utterance of “ahhh.” This is rude in general, but seems even more appalling when it follows a sip of alcohol.
Women AND men should take care not to spill any drink on their clothing or body. If a female is offered a sip by another female, especially if it’s from an old college sorority sister, she should slowly bring the flask up close to her nose, take a whiff of the alcohol inside, and then take a very small “baby sip,” just in case it contains something she is not accustomed to. Any woman would not want to have her mouth and her senses overwhelmed by the intensity of an ultra harsh alcoholic beverage, have to spit it out, thereby embarrassing herself and making a spectacle.