I think I've heard "dressed like a bum" (realised it after GS's post 13) and, for some reason, can easily imagine someone saying "dressed like a vagrant" (even though this word is new for me), but I'm curious now whether it's true considering the word "homeless". "She's dressed like a homeless person"?
Maybe I should explain my question in post #18 and how it is related to the initial question since it seems to be drifting off-topic. The main reason why I asked about the word for homeless people with the negative connotation is that I thought that, knowing the word (or words), it would become clear to me how people speaking English might show their strong disapproval at how people are dressed. It was rather silly of me not to put the question this way from the very start, but unfortunately this bright idea came to me much later. :-( Now I don't know if I should open another thread and make a more precise question, or whether it's a good idea at all to start a thread on such type of languge (which may be offensive) on this forum. Myself, I see it from the perspective that a language is a natural thing and it may not always be politically correct but still commonly used.
And it doesn't mean that I'm going to use the offensive languge (which I already mentioned in post #4). It's just a mere curiosity.