Where I came from, when someone is ‘sad’ they are what Americans would call a ‘loser’. They are not unhappy because of a specific event (one meaning of ‘I am sad’) but they are pathetic in general.
What, in your neck of the woods, does ‘I am a sad person’ mean to you?
Don’t worry. I do that all the time. In fact probably the majority of my posts break at least one rule of a thread’s theme because I didn’t pay attention to the OP or title. All you did was confirm what I said in the OP, which didn’t seem out of place at all.
It would depend very much on the context. If it were used to describe someone who had just had some sort of unpleasant experience then I’d assume it meant upset, sorrowful, *mournful * etc. If it were used more generally in an expression like he’s a sad specimen, then I’d assume it meant pathetic loser.
I have seldom heard “sad” to mean “loser.” It usually means unhappy. If I hear, “he’s a sad case,” it could mean a loser, but in a really tragic way. That is, expressing pity rather than ridicule.
Long, long ago, there was a cartoon soldier named Sad Sack. Now, there was a loser, right down to his socks.