Probably the worst form of evangelism is street evangelism. It comes in several forms.
The first type is Bullhorn Evangelism. I know that some people do get saved through these sorts of street preachers, but for every one person who receives eternal life, hundreds more are turned off by such a presentation of Christ and Christianity.
The Evangelism of Red
When I was growing up, there was a street in town with lots of bars on it, and it had a regular patron named Red. And though he was often surrounded by empty beer cans and other assorted trash, he never entered a bar and never had a drink. The bottles and cans were thrown at him by drunk revelers. Why? Because every night he walked up and down the street, waving his Bible in the air and shouting his version of the Gospel through a bullhorn. When people threw bottles and cans at him, Red loved it all the more, because he thought he was enduring persecution for the cause of Christ.
Looking back now, I wonder who was persecuting whom?