This illustration means that every parent nowadays are worried for their children because all they children do is hangout with their friends and parent knows that these friends can be his/her worst enemy. All the bad habits such as smoking, which could cause lung cancer, tumor, many other diseases that could put a person's life on line and once a person get this kind of disease, he/she will may die, Alcohol/ Drinking Habits, which also cause fatal diseases. This pictures is explaining that's how everyone is always surrounded by friends or in other words your worst enemy.

Not Every friends of yours is bad, you just have to pick the right person, don't just hangout with everyone.