(pali + english, derived from b. Sujato trans.) http://lucid24.org/an/an07/an07-v05/index.html#s64
(b. thanissaro eng. trans) https://www.dhammatalks.org/suttas/AN/AN7_60.html
The passage in question:
“And further, an enemy wishes of an enemy, ‘O, may this person not profit!’ Why is that? An enemy is not pleased with an enemy’s profits. Now, when a person is angry—overcome with anger, oppressed with anger—then even when he suffers a loss, he thinks, ‘I’ve gained a profit’; and even when he gains a profit, he thinks, ‘I’ve suffered a loss.’ When he has grabbed hold of these ideas that work in mutual opposition (to the truth), they lead to his long-term suffering & loss, all because he is overcome with anger. This is the third thing pleasing to an enemy, bringing about an enemy’s aim, that comes to a man or woman who is angry.
(3) “Again, an enemy wishes for an enemy: ‘May he not succeed!’ For what reason? An enemy does not delight in the success of an enemy.  When an angry person is overcome and oppressed by anger, if he gets what is harmful, he thinks: ‘I have gotten what is beneficial,’ and if he gets what is beneficial, he thinks: ‘I have gotten what is harmful.’ When, overcome by anger, he gets these things that are diametrically opposed, they lead to his harm and suffering for a long time. This is the third thing gratifying and advantageous to an enemy that comes upon an angry man or woman.
In the other 7 cases in the sutta, specifics are given so it's clear what the person who wants the enemy to suffer, how their anger sabotages their desire and tends to get the opposite result. In the case # 3 above however, it's not clear what the Buddha had in mind for specific examples. I can think of some hypothetical situations that would meet that criteria, but they would just be guesses.
Anyone think they know exactly what is meant here?