Work your arse off
Definition 1 of 1
Pro Tip 1/3British Origin
Originally British English, may not be well understood in countries where British slang is not common. 
He's from the UK and says he 'works his arse off' all the time.
Pro Tip 2/3Informal
Very casual, best used with friends or in informal settings, not in formal or professional contexts. 
Whenever we hang out, she always mentions how she 'works her arse off'.
Pro Tip 3/3Emotionally Charged
Expresses strong feelings, usually pride or frustration, about the hard work being done. 
After the long week, he exclaimed, 'I've been working my arse off!'