A euphemism (another word for) giving a blowjob. Comes from the scene in Harry Potter and the half blood prince when Ginny and Harry are talking, and Ginny says "shoelace" and bends down to tie Harry's shoelace, but it looks like she's going to suck his cock.

The Chinese, famously, exclusively wear sandals. Therefore, to tie the Chinese shoelace is to do the impossible.

When one is asked to tie someones shoelace, they have just been asked to "netflix and chill, these dogs will explain for me.