"He closed his [opening] prayer, and began to preach; but evidently his audience were not disposed to hear him. Before many sentences had been uttered, missiles began to fly--at first not of a very destructive character, being refuse--vegetables, potatoes, turnips, etc., but before long harder materials were being thrown--brickbats and stones, some of which reached him and inflicted slight wounds. He stopped, and, after a pause, cried out, 'Boys dear, what's the matter with you to-day? Won't you let an old man talk to you a little?'Quoted in Spurgeon, Lectures to My Students, p.248.
I must admit — I've never had that happen while I was preaching. Maybe I'm not preaching hard enough or out in the 'open-air' enough, then.