我姓任也认不出你
[wŏ xìng rèn yĕ rèn bù chū nĭ]
In literal terms, 'My surname is Ren (任) yet I still don’t recognize you' may mean that even if we’re well-acquainted to the level that I know your last name, it is difficult for the owner of the username to identify you, suggesting unfamiliarity, perhaps in the context of online identity where anonymity reigns.