The city sucks. @o@?!

My English teacher once told me that the city he stayed "sucked". I thought we could use this word to describe anything we don't like. But later I found that this word should be used carefully. In one movie I saw before,there was a conversation going like this: a little boy picked up his toy and... 顯示更多 My English teacher once told me that the city he stayed "sucked".
I thought we could use this word to describe anything we don't like.
But later I found that this word should be used carefully.
In one movie I saw before,there was a conversation going like this:
a little boy picked up his toy and said,"this stuff sucks".
Then his mother turned around and said,"Watch your language".

Is this word a kind of four-letter words (vulgar language)?
Or are they commonly used among boys but a lady had better not to use it,
like the Chinese word "爽"?
更新: Thanks you guys for your clear explanations.
I'll think twice before I use this word.
12 個解答 12