In these lines, we see what Harry's objective is in hanging out with people who are not particularly desirable. He tells us that the only reason why he hangs out with lowly people and behaves in an unadmirable way is because he wants to create contrast between his present behaviour and his much more restrained future. He believes that, if he acts extremely irresponsibly now, then it will seem all the more impressive to everyone when he changes his ways and decides to be a proper, responsible king.