What it means for something to be objective is for it to be the sort of thing where if there are opposite positions taken, the law of noncontradiction applies and one person must be right and the other wrong. So, for example
1) The cat is on the mat.
2) The cat is not on the mat cannot both be true once we know which cat and which mat.
Now in a subjective matter, someone who says
3) McDonald's Quarter Pounder is better than Burger King's Whopper
and someone else who says
4) Burger King's Whopper is better than McDonald's Quarter Pounder
don't really contradict one another, because each implicitly includes a "for me" clause into their respective statements. The law of non-contradiction doesn't apply here.
Let's take another pair of cases.
5) Belching after dinner is rude.
6) Belching after dinner is polite
is again subjective, not because it is an individual judgment, but because it is a societal. When we say these things, we assume that we speaking on behalf of a social group of which we are a member. So if cultures differ on this, there is no real contradiction, and neither party has to be wrong.
7) More than 50% of the abortions done in America today are done without adequate moral justification.
This is a tough question about which people might disagree. One's beliefs on this matter might be caused, to a large extent, by one's religious and cultural background or beliefs. It's a moral toughie, one we can argue about until the cows come home. Does that make it subjective?
You have to remember, though, in ethics class we deliberately pick out tough issues to deal with, ones where there are moral considerations on both sides. There are other moral statements, however, that are not so tough, such as
8) Whoever sliced the throats of Nicole Brown Simpson and Ronald Goldman did the wrong thing.
If you remember the OJ trial, you will remember that everything in that trial was controversial, except for the moral judgment implied in 8. Johnny Cochran would have been out of his tree if he had tried to acquit OJ on the grounds of justifiable homicide. But if you are a moral subjectivist, you hold that all moral judgments are subjective, including 8. Ayer's position implies that all moral statements are either true for a person or for a culture, and not across the board. When you think of all this includes, I think it is tough to swallow, although some people try.