Something which complete assholes and bitches say to condone their douchebaggery behaviour. They have no problem resorting to devious tactics to get what they want, even if what they do harms other people . The same people are likely to also use the phrase 'it's a dog eat dog world'. They believe that behaviour which is deceitful or not fair is acceptable during an argument or competition. They must win at any cost.
In order to go on a date with me, I'll trick her into believing that her boyfriend is seeing another woman.
Did you tell her lies about her boyfriend so she would hate him and go out with you instead?
Of course! All is fair in love and war.