Don't use this as a pretext - let's stick to what's in front of us.
Tips
history
Wu Jianren's late-Qing novel 痛史 has a scholar say: "I get worked up and scold them - this is what you literary folks call 借题发挥." The phrase describes the writer's trick of using any topic as a launchpad for unrelated arguments.
usage
Usually slightly negative - implies the person is opportunistic or petty, using a minor trigger to vent larger grievances.
