Seriously mate, no fighting art will teach you to 'beat up people bigger than you' without serious dedication and training. And why would you want to do that. Being able to defend yourself is the issue should a situation arise. For strength and from your attitude I think you probably mean big arms just go to a gym and lift weights.

From a self defence point of view I would reccomend Tae Kwon Do (preferably WTF not ITF). By doing this you will learn to fight in a ring and some very useful and effective self defence techniques.