After several brief-but-quickly-resolved misunderstandings between an English major friend of mine and me, I've found that the main basis was a bit beyond mere lexicology -- that it was on the emphasis.
Given a normal statement: A X B (where A is subject; X is verb; B is object), the emphasis can be on any one of the three elements. The focus could be on A, X, or B, which is usually determined by preceding sentences and context. However, often the misunderstanding would arrive when one party would say "the opposite of AXB" to the other. What possible ways can that be interpreted?
Basically, switching the "agent" of the sentence, which can be done in one of two ways. So instead of "A X B", we could have "B X A" or alternatively "A is X by B". Here, switching A and B seems natural in the following examples:
i. I bit the dog
⇒I was bitten by the dog
⇒The dog bit me
ii. She scares me
⇒I scare her
⇒She is scared of me
This is done by simply negating the sentence. However, this usually ends up not expressing a whole lot of information, especially outside of context. Also, it's not clear whether the verb or the object is being negated:
i. I'm eating lunch
⇒I'm not eating lunch (I'm doing something else to lunch instead)
⇒I'm not eating lunch (I'm eating something else instead)
ii. I kissed a girl
⇒I didn't kiss a girl (it wasn't a girl I kissed)
⇒I didn't kiss a girl (it wasn't a kiss that I shared with the girl)
However, both interpretations could be simultaneously true: "I'm not eating lunch" could mean both that it isn't lunch AND that I'm not eating. I could be chewing gum, for example. Also, it could be the subject that is being negated - It could have been Henry who was kissing the girl. ...or Larry who was massaging a client. This form of "opposite" is by far the worst choice.
This is one that I tend to do sometimes, but it doesn't always make sense. I would replace the verb with another one that had an opposing meaning. So instead of A X B, we now have A X-1 B.
i. I love technology ⇒ I hate technology
ii. Tommy killed his computer ⇒ Tommy revived his computer
Of course, this practice breaks down when you're given verbs with no clear antonym:
iii. I eat worms ⇒ ? I grow worms
iv. Sally kicked the desk ⇒ ? Sally rubbed the desk
Most verbs seem able to work with some sort of negating prefix like un-, in-, etc.
Usually, conversations will hint which way the sentence should be negated, as so:
M: Hey, did you hear? Q got sacked!
N: They way I heard it, it wasn't Q...
M: Oh, you mean it was P! Q's corporate nemesis!
Now, see what can happen without those cues:
T: So I'm pretty sure she likes me.
S: Really? 'Cause I think the opposite, actually.
T: You mean, (a) She hates me.
(b) She likes sby else.
(c) I like her.
(d) none of the above.
(e) all of the above.
Note that in this specific case, (b) doesn't make a lot of sense, unless there is implicit knowledge between the speakers that the T, the girl and some other person R were in an intimate relationship triangle. (d) and (e) are there out of fond memory of an exam I wrote a few years ago. So the only real choices are (a) and (c). But the problem is, (a) and (c) are mutually exclusive; either one could be true without affecting the other. And therefore, S' remark about "opposite" is poorly phrased for being ambiguous.
Instead, S should have either said: "Really? 'Cause I think she does the opposite," indicating that the verb should be replaced, or, "Really? 'Cause I don't think she's the one doing the liking," indicating that the subject and object should be switched.
So from this, what I've found to be more-or-less true, is that whenever I'm speaking about "opposites" with my friend, I tend to focus on the verb, since grammatically, the verb is the matrix of the sentence, whereas my friend tends to focus on the actors, since semantically, they're the most important.
As a final note, negations are an extremely large topic in linguistics; there's a fat tomb sitting in certain libraries, called A Natural History of Negation. Not a fun read, but extremely thorough.