particle used to exaggerate certain adjectives, in particular 神经 shén​jīng兮 xī兮 xī (nervous), 脏兮兮 zāng​xī​xī (dirty), 可怜兮兮 kě​lián​xī​xī (pitiful), and 惨 cǎn兮 xī兮 xī (miserable)

看他那副可怜兮兮的样子，真让人心疼。