A customer at work started yelling at one of my co-workers, and everyone else just stood there looking at them.
Some crazy customer started screaming at someone I work with, and all the other staff members just stood by and said/did nothing.
この場合、次のように言うと良いでしょう。
ーA customer at work started yelling at one of my co-workers, and everyone else just stood there looking at them.
「職場でお客さんが同僚に怒鳴り出して、他の人はただ彼らを傍観しているだけだった」
just stood there looking at ... を使ってただ傍観していたことを表現できます。
ーSome crazy customer started screaming at someone I work with, and all the other staff members just stood by and said/did nothing.
「ある狂ったお客が一緒に働いている人に怒鳴り始めて、他のスタッフはただ傍観して、何も言わなかった/しなかった」
just stood by and said/did nothing で「ただ傍観して何も言わなかった/しなかった」と言えます。
ご参考まで！
カナダ 
