Ones with known bias or agenda... e.g right-wing sources like Breitbart which mostly consists of ranting loonies presenting non-factual facts. In fairness I would say the same of extreme left-wing sources but I have never actually seen one so can't really comment.
If I were commenting specifically on the UK - I would say a bad source is. 'The Sun' - utter trash. Generally speaking though our news is pretty balanced.. sticks to facts without engaging in bias - generally professional.. We tend not to see the mudslinging and trashiness - sure we have politicians mud-slinging at each other but the reporter or interviewer remains unbiased.
Baba 