我是外星人我要回火星
[wŏ shì wài xīng rén wŏ yào huí huŏ xīng]
'I'm an alien, I want to go back to Mars' can suggest the person feels different or out-of-place here on Earth; perhaps feeling like they don't belong. It's also playful and whimsical indicating love for Sci-fi/fantasy cultures.