Чмо: weirdo, bum, idiot, jerk (etc.)
Чмо isn't a word I use much. I could never get a handle on its meaning, and I could never figure out how to decline it. But then I discovered two wonderful things: чмо is what linguists call асемантичное ругательство — a derogatory word for a person that doesn't have a fixed meaning — and it doesn't decline at all.
Of course, Russian being Russian, it's a bit more complicated than that. There are a few more or less standard meanings of чмо. One is a person who is shabbily or inappropriately dressed: Девушка приходит на работу как чмо, даже волосы не расчёсывает. (The young woman comes to work looking like a bag lady. She doesn't even comb her hair.)
Another meaning is someone who behaves oddly or looks weird. Some people use чмо kindly in this sense. Парень — чмо, но очень талантливый (The kid is a kind of a dork, but he's very talented).
Others use it as a stronger pejorative for a weirdo: У станции метро стоит какое-то чмо, матерится, чего-то хочет от меня (So there's this wacko standing by the metro station, swearing his head off and asking me for something).
And then чмо can be used to describe someone stupid, naive or easily deceived: Сосед хотел, чтобы я вкладывал деньги в его дело. Я что, похож на чмо? (My neighbor wanted me to invest in his business. Do I look like a total chump?)
Finally, чмо is a nobody, a worthless person, a jerk. Often the word is combined with intensifying adjectives, like последнее (worst), зелёное (literally green), болотное (literally swampy) or тупое (dumb).
So where does this weird word come from?
The theories about its origins are as interesting as the word itself. One scholar, M.T. Dyachok, has done the heavy etymological lifting and thinks it came from the Yiddish shmuck, which means, among other things, a fool. It wended its way via Odessa and criminal groups into camp slang, where it came to mean a prisoner who cooperated with the authorities.
In the armed forces, it garnered the meaning of an untidy or shabbily dressed soldier. Somewhere along the way, чмо got mixed up with the native Russian words чмарь and чмырь (dirty, grubby person). Today's чмо seems to combine all of these meanings into one multipurpose, insulting noun.
The strangest thing about the word is that it refers to a person but is neuter and doesn't decline. This has led armchair etymologists to speculate that it's actually an abbreviation. Here Russian folk fantasy is at its most creative. Чмо, people say, is an abbreviation of человек, мало образованный (poorly educated person); человек морально отсталый or опустившийся (person of low morality); человек мешающий обществу (person who disrupts society); or more recently — человек Московской области (person from Moscow oblast — that is, a provincial).
Another theory is that чмо came from the Great Patriotic War as an abbreviation of часть материального обеспечения (field-support unit). These were the soldiers who brought supplies to the front lines and were allegedly reviled by the fighting men for their poor performance and less dangerous positions.
And now some opposition-minded people use чмо to mean член молодёжной организации (member of a youth organization) with a definite pejorative connotation. In this context, чмо поганое would be a filthy little collaborator.
That's definitely not Joe Shmo.