笑面如渣
[xiào miàn rú zhā]
It translates roughly into 'A smiling face as despicable/bad as refuse,' reflecting a kind of sarcastic self-deprecation. The creator wants to show that he/she may act happy on the outside but inside might feel differently or may actually be someone with low moral character. In essence, this could represent an unflinchingly cynical or critical outlook towards oneself.