A guy that breaks up with his gf and talks shit about her, then goes tells another girl he loves/ likes her. And then he gets back with his gf and don't tell the other one and still fucks with them.
Usually used, as most French terms - je ne sais pas, ennui, to describe that certain something that is beyond normal language.
Nowdays it is often referred to (incorrectly) as X-factor
However Savior faire suggests a certain style, accomplishment and refinement. A person who has Savoir faire is naturally suave and classy, or has the innate abiilty to do or say the right thing at the right time.
The great Irish wit, Oscar Wilde, has considered to have Savoir faire, although he probably would have said that he was more Laisser faire (i.e. lazy, disinterested or libertine)
or in a more modern context;
The actor George Clooney can be said to have Savoir faire