There are, without any doubt, situations where you can't win for losing.
Often, these involve situations with a bunch of considerations or variables steaming in from a wide variety of directions.
Recently an individual engaged in a behavior in my presence that left me significantly uncomfortable on a couple of different fronts. I am relatively certain they meant no offense (or at least certainly hope that it was not some Machiavellian plot to annoy). I was much too tired to even snarl (and diplomacy was not even in the cards at that point). At the same time, I was aware this person had a plethora of other issues through which to work. And finally, I was (or should have been conscious enough to realize) that awkward behaviors will stay awkward until some sort of subtle or dramatic lesson is presented.
In such situations, misplaced kindness (and in honesty, exhaustion) may dictate a "grin and bear it" approach followed by kvetching to trusted friends - with a greater or lesser degree of enthusiastic venting. While far more constructive than simply smiling and internalizing the irritation, this approach is likely less than ideal.
The problem with this approach is that it facilitates the misbehavior du jour, even if the motivation is that the individual has "troubles enough." In other words, by failing to mention the issue one might be considered to enable further such faux pas.
Depending on the individual du jour, it may be wiser to express objections privately (if the party is well enough known to be trusted) or publicly (in case witnesses are desired/handy). Obviously, that determination is pretty darned individual - but if in doubt, public but polite is probably the best opener. One can, after all, always become more painfully clear in expressing an objection.
On the other hand, while certainly a form of effective communication, a full-bore and detailed examination of the objective behavior in an acidic command voice is likely unkind, if memorable. And the shock of the delivery may well overwhelm the message, particularly when an individual is busy multi-tasking other life issues. It is far to easy to misinterpret a detailed "stop that" as "s/he is attacking me."
This is true even for folks with merely average issues to process, let alone those with a double-high stack - leaving this second approach as limited to special cases where one simply wishes to permanently drive off the offender through non-physical means. I.e., a fairly limited set of applications.
Finally, the whole notion of getting physical over minor to medium social errors is highly individual. I've a fairly high (it has been suggested unsafely so) standard for graduating to such means - but I recognize that others life experiences and training/education may well leave them with different, yet valid, set points. As a personal policy, I have come to the conclusion that I am deeply disinterested in discovering those set points in others (particularly and especially in those others that I have reason to believe could effortlessly break me in half sans tools).
So. Kindness v. Confrontation may, at times, mean that kindness involves some level of confrontation...and at others, that kindness dictates simply venting to friends and moving on.
Your mileage WILL vary.