get off your arse （用于强迫自己开始做事情）做起来，快行动

【例句】
Tell her to get off her arse and do some work for once.
告诉她做起来，快行动，她总要有那么一次做点事吧。

The job will never be finished if you don't get off your arse.
你们不来干，这活永远完不了。