Not cricket
Definition 1 of 1
Pro Tip 1/3British Origin
Understand that 'not cricket' comes from the sport, symbolizing fair play, common in British English. 
Skipping the queue is simply not cricket in British culture.
Pro Tip 2/3Cultural Connotation
It carries a tone of moral disapproval, suggesting an action is against societal norms. 
Talking behind someone's back is not cricket.
Pro Tip 3/3Informal Phrase
Used in informal situations; might not be suitable for formal documents or discussions. 
Claiming credit for others' work? That's not cricket.