In British English, if you bollock someone, you tell them off in an angry, sharp way — you make it very clear you do not like what they have done. It is informal, and it is rude. You would not put it in a school essay, and you would not say it to a teacher. Friends and workmates might say it to each other (“The boss bollocked me for being late”). Though actually the word first meant a testicle — literally a “little ball” — and that older meaning is still alive in bollocks, which British people also shout when something goes wrong. The angry-telling-off meaning grew out of that rough body-part talk. American English almost never uses this verb; Americans would say tell off or chew out.