无敌屯炮
[wú dí tún pào]
It's quite unique; '无敌' (Invincible), '屯' (to amass or save up), '炮' (cannon or figuratively a powerful attack). Taken together, it may express someone feels untouchable and has saved up a powerful 'attack'. Might also refer to online gaming context where this kind of expression would make sense.