Of course I will ask for another glass (Hope he/she did not give me the dirty glass with purpose). Most of the time, people make mistakes like this. Therefore, asking for another clean glass is not going to cost anything. Perhaps she will apologize for her mistake and will give me another clean glass.

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I have a relative who is not so good at housekeeping (I'm being nice). I may actually clean the glass myself, as I'm not so sure any of her glasses would be any cleaner than the first one. I would make some sort of comment like, "excuse me just a minute while take care of something. I know you didn't notice, but the glass was a little dirty. I'm going to clean it out and just fill it with some tap water." I would say all of this on my way to the kitchen.

It would depend on how close a friend she is. If we were in an informal situation and we were close I would just mention it and maybe just get a clean glass myself. If we had a more casual friendship, I might take a few polite sips so as not to hurt her feelings, especially if I didn't know her too well yet.

It would also depend, if we were part of a group of people, and my friend was the hostess, even if I were close to her, in that situation I would remain silent until I could discreetly make her aware of it so as not to embarrass her in front of her other guests.

So I suppose whether I tell her or not and how I tell her, depends on the degree of friendship with her and the social situation we are in at the time.

Hold it in your hand for a very long time and put it down when they don't notice. Pretend to take small sips if they are watching. Say you need to go to the bathroom and dump it there. If need be, dump some, and dilute it slowly with water and decrease the amount little by little until there is none left to be discreet.

"Oh sorry this glass has a spot that did not come out in the wash, do you have another"

This is a polite way to bring it up without sounding nagging. I would be horrified to think as a host someone may not mention it to me if I missed something like that. I would expect my guests to say something, so I would say something if I was in that situation.

If I were at my friend’s house and were handed a not-so-clean glass with a beverage in it, I would likely say “Oh no, I don’t mean to be wasteful, but it looks like your dishwasher failed you on this glass”. That way I am not attributing fault to her but to the workings of technology. Or, since I am pretty familiar with my friends’ kitchen, I would likely just go to the cabinet myself and get a new (clean) glass or grab her sponge and some dish soap and clean the glass myself. Not a big deal. The friend may have just taken the glass out of the dishwasher before she handed it to me and all dishwashers sometimes miss spots on the dishes. Even if she had taken the cup from the cupboard, I would not judge her, because I know it could be easy to overlook a spot on a glass if you are in a hurry when putting away the dishes. Overall, it’s important to know the circumstances before making snap judgments about someone’s hygiene. I remember I ran into this problem multiple times in my grandpa’s house, after my grandma started living in a nursing home. My grandpa, then in his early 80’s, had a hard time seeing and insisted on washing all dishes by hand. Unfortunately, most of his cupboard was full with stained or not fully rinsed dishes. I typically made it a habit when I visited him to take out the dishes and give them a good scrub down so that he would have clean dishes to eat and drink from.

I just drink my drink and ignore unless it's dirty with food residue or something like that. I'm not too picky about the condition of my glasses, silverware, dishes, etc. As long as there isn't old food that I wouldn't eat myself on it, I really don't care. I'm fine with reusing stuff.

It would depend on how dirty it was. If it had obviously not been washed since the previous use or had crustiness on it, then I would ask for another glass. Or depending on how close of a friend, the person was, try to sneak into the kitchen to switch out the glass myself. I would definitely be tactful, and if there were other people present, not say anything to alert them to the issue.

If the glass just had a couple spots on it, on the other hand, I would probably just drink out of it. Especially if it was a good friend - if so, we probably have traded germs a few times before.