甩开膀子

shuǎi kāi bǎng zi

to throw off inhibitions

to go all out

甩

shuǎi

to throw

开

kāi

to open (transitive or intransitive)

膀

bǎng

old variant of 膀[bang3]

子

zi

noun suffix, as in 椅子[yi3 zi5] "chair"