谁让我当备胎我就让谁爆胎
[shéi ràng wŏ dāng bèi tāi wŏ jiù ràng shéi bào tāi]
Translating into 'Whoever makes me the spare tire, I'll make sure their tires blow out', it is a way of saying 'Don't toy with my feelings or play me for backup; it'll backfire!'. It expresses frustration with those taking advantage in a relationship context where one person uses another as a 'safety option' while holding out for someone else more desired.