蛋疼不是病疼起来真要命
[dàn téng bù shì bìng téng qĭ lái zhēn yào mìng]
A rather crude expression, directly translated as 'testicle pain is not an illness, but it can be really killing when in pain'. Often used figuratively by young Chinese males on the internet to talk about something troublesome or nagging yet not serious enough.