When Robin Hood comes across the foresters in the prologue, they are feasting in the forest rather than protecting the king's lands. They are feasting like pigs as well, for they all share a huge pasty or meat pie and eat it by "thrusting" their hands inside it. One of the foresters shows additional lack of table manners by talking to Robin Hood with his mouth full. Worse, he insults Robin Hood. Although Robin is a grown man, the forester makes fun of him and calls him a "little lad."
In short, the foresters make a "fine show," lolling around under a tree eating, drinking, and insulting Robin Hood when they should be doing their jobs.
They go on to agree to a bet with Robin Hood that he can't hit a hart, but when he kills it, winning the bet, they refuse to pay. Instead, they threaten to beat him and to turn him in for poaching. In such ways, they show themselves to be dishonorable people.