The phrase "obvious culprit" refers to a person or thing that is easily and clearly blamed for a particular problem or situation. It means that their involvement or responsibility is very apparent and easy to see. Full definition
So what causes teeth staining and well the answer to this is almost everything we come in to contact with will stain the teeth and this ranges from the most obvious culprits like coffee, tea and nicotine to things like cherries but the thing isnot to get too stressed about as there's a good solution. (pillowspot.com)
The most obvious culprits of creating hate against Muslims in general has been the politicians and the media. (religion.blogs.cnn.com)