This is really not that big of a deal. First of all, pop culture tropes get added to the dictionary all the time, it shouldn't be a surprise that this would happen eventually. People who use these words don't care if they're "actual" words. Besides, do they really seem like the type of people who would pick up a dictionary to decide what words to use? Is it really going to hurt you if you own a dictionary with YOLO in it?
Also, words change definition all the time. Swag meant something at one point and now it means something different, might as well acknowledge that the meaning has changed. This isn't really anything new and you have to admit that slang has always been dumb. Swag isn't any worse than 'radical' or 'cool' or what have you. All words that are part of the lexicon and were started by dumb teenagers. Dictionaries have to reflect words that people use, and whether or not you like it, people regularly use those words now.