Russians spend every day of their lives hopping between two parallel universes. Here are some examples:
They speak two languages: polite Russian, and an earthy colloquial pronounced "maht". They talk polite Russian to neighbors, coworkers, friends, and some of them talk maht at bars, or when they tell jokes, or when they're with their buddies. A well-bred Russian may understand maht, but will not speak it.
Russians live with two social lives: an external projection to neighbors and coworkers (where they've learned over the years to be careful what they talk about), and home life, where you can safely complain about issues, lack of services, the failing economy - whatever.
Like most Europeans, they have two ways of referring to "you". You say "vui" to be polite, but after you know somebody for a while, they can ask you to call them "ty". Of course, they may never get around to asking you, and it's very rude to assume "ty" otherwise.
And Russians have two very passionate spiritual lives: the Russian Orthodox Church, and their horoscopes, which they're all hooked on. You can have a very deep discussion with Russians about your sign and how it affects your life, and you can then go to church with them and see the depths of their Christian beliefs.
Russians are very adept at knowing which universe they're currently in, and acting appropriately. I, however, am not very good at knowing which universe I happen to be passing through at any given time. I see it all as one big Russian universe - I don't know which words, which subject, which "you", and which spiritual acts belong where.
For example, I would never tell my grandma, or my priest, an f-word joke; I know it would be offensive to them. But the Russian f-word sounds the same as any other Russian word to me. I asked Irina to translate an off-color joke, but because there was no polite Russian translation, and because we were in a polite Russian environment, and because my joke left no wiggle room for innuendos, it turned to out to be offensive instead of funny.
Another example: we went to an orthodox church, and I asked if there was a Russian Saint Dennis out there. When the priest told me that my namesake saint was also born in October, I said "wow, he's a Libra like me!" thereby demonstrating to the priest my ignorance in universe identification.
So now I know how to judge my ability to speak and understand Russian: when I'm able to recognize which universe I'm in, and act appropriately. Until then, I'll stumble my way through, holding on to Irina for dear life.