One of the tricks of playing a character in a fantastic environment is that there are quite often some form of mental coercion spell or skill that should, by rights, be able to change your PC's mind about something. While this seems easy in theory - albeit a bit annoying to lose some PC control - it actually can be quite troublesome. We're not designed to switch gears emotionally so rapidly and consciously in reaction to a die roll. We've no experience of it. So it can be hard to figure out what to do about it.
Now while many games have an unwritten rule that PCs shouldn't use emotional/mental control spells or coercive skills on each other, some games really need to have it on the table. This is especially the case in games like Vampire: the Requiem (even more so the new Blood & Smoke version) as there are a lot of ways to coerce each other and the setting pretty much calls for it.
So what to do?
For starters, make sure the entire group is on the same page in regards to it. If players enter a game knowing that they are subject to certain powers and/or skills, even by other players, then that reduces a lot of headache.
On an individual note, players should put some thought into their character's specific reaction to certain mind or emotional controls to figure out how they might roleplay it. If a magical spell could send a normally stoic individual into a beserk rage, then it's helpful to know *how* that *particular PC* might enter a beserk rage and what that might look like. With that extra bit of mental preparation, you'll be far less likely to sit their slack-jawed and confused as you hurriedly try to figure out what your PC might do (which has happened to me several times).
NOTE: Even with player agreement be aware that generally most players are more amenable to the idea of powers being used rather than skill rolls as another PC's dialogue might be so ludicrously ineffective that it really breaks character consistency to be affected by it. After all, a player could couple an exceptional success on a seduction roll with the phrase: "Sit on my lap, Darl." Something that isn't very effective for most personality types. If players can roll social skills against each other you should ensure that the player on the receiving end gets to dictate effective dialogue / tactics. Therefore the PC-Thug-Coercer who wants to seduce the high society girl has to choose whether he's willing to stoop to the expensive dinner and philosophical discussion that would be necessary to seduce her. Effective social manipulation depends on playing to the target's personality, after all, and not to the user's.