He was mingling with the wrong sorts of people.
Not just mingling, mind you, but welcoming them. Eating with them. Clearly his parents had not brought him up well, teaching him that he would be known by the company he kept. He did not keep good company. Jesus didn’t just welcome these sorts of folks, he sought them out which sets the religious elite to grumbling. Jesus spent a lot of time with the kind of riffraff most of us try to avoid. “This fellow welcomes sinners and eats with them” they tut-tut.