Often, those who stare say 'laowai' to which I would usually repeat the word 'laowai' and point at myself with a slight smirk (as if to say 'oh yeah, you're right, how amazing... I'm a foreigner, so what?!').
After that, they'd always embarrassingly laugh knowing they'd been rumbled. A slight gleem of satisfaction regarding an annoying habit of the Chinese (by our standards) that let them know they'd been rumbled using a humorous tactic. Made me feel better, anyway.