Assuming you are referring to Matthew 5:38-42 (NIV) :
38 "You have heard that it was said, 'Eye for eye, and tooth for
tooth.' 39 But I tell you, Do not resist an evil person. If someone
strikes you on the right cheek, turn to him the other also. 40 And if
someone wants to sue you and take your tunic, let him have your cloak
as well. 41 If someone forces you to go one mile, go with him two
miles. 42 Give to the one who asks you, and do not turn away from the
one who wants to borrow from you.
You could explain this rhetoric, but if we look at the examples He uses, it does not have to be rhetoric but can also be literally. Let's take a look:
If someone hits you on the right cheek, the attacker hopes he won with just one hit (this was usually a hit with the back of the right hand, not very hard, just to scare you off) . If you fight back, you are as low as your attacker, if you do nothing (which he aims for), he wins. However, Jesus tells here: "turn to him the other also". How would the attacker feel right now? He did not win, and he has to hit a second time (this time really on purpose, and if he hits he can now hit hard. (try it once, back of your right hand on someone's right cheek, if he turns his head so you can hit the left you can hit full power)
The second example Jesus gives, is similar. Back in the days of Jesus people wore most of the time only two pieces of clothing, your tunic and a cloak. If someone asks for your tunic, you know you are naked under your cloak. Which, again, hurts only you and will give you won. But if you do also give your cloak, how would the one requesting for the tunic feel now?
The third example Jesus gives, is similar as well. If you were forced to walk one mile (usually by the legal power), a soldier would go with you to check whether you walked the mile. (often you had to carry a burden as well, but anyways) When you walk just the mile, it hurts only you and you have accepted your punishment. However when you walk an extra mile the soldier checking you walked the mile had a problem, he was not allowed to punish you more than the he was ordered to.
Is Jesus merely saying that we shouldn't seek revenge, or is he advocating pacifism?
I would say Jesus is indeed saying that we should not seek revenge. He challenges us to be smarter than your opponent(probably not the right word) and show them that you are not controlled by him, and therefore not do whatever they tell you, but live for the living God.