grass up
phr. v..phr. v.. to tell the police or someone in charge that another person has done something wrong. You use this when you think someone is being a 'snitch' or a 'rat'.
phr. v.. to inform on someone to the authorities; marked British informal / slang, often carrying a negative connotation of betrayal within a peer group.
He refused to grass up his friends to the teacher.
The thief was caught after his partner decided to grass him up to the police for a reward.
In certain communities, the social pressure not to grass up one's neighbours remains significantly stronger than the fear of legal repercussions.
usually followed by an object (the person being reported) and often used with 'on'.
this is a highly regional British term; compare it with the American 'snitch on' or 'rat out' to show how different dialects handle the concept of informing.
He grassed up to the police.He grassed them up to the police.this phrasal verb usually requires an object to specify who is being informed on.