In my opinion, the farmers' former friends were in the wrong. When two parties have a dispute, the first step is to step back and rationally, calmly discuss differences of opinion. If this fails, the next step is to settle the dispute in a court of law. In no circumstances is it appropriate for one of the parties to personally inflict physical punishment on the other party.
Although friends enjoy playing pranks on one another, forcing this guy to eat his beard over a lawnmower crosses the line. It seems like he agrees, because they are now former friends. I can't envision any scenario in which the dispute was so important that they should have taken such a drastic step with him.
It is abuse to make a person ever put another thing in his or her body. Forcing someone to eat bread or anything else is an example of abuse. People should be more respectful of the rights of others. This man needs to learn that these are not really his friends if they are willing to do something like this.
There are sometimes disagreements among friends, but it is never right to physically assault someone. Even thought the news topic of a man being forced to consume his own beard may sound amusing, it involved sharp weapons and left him with a wound to his throat. He could have been seriously injured.