finding the proper word?

I frequently have the problem of not knowing the word or term that best describes the phrase im thinking of, like the definition of a word in a dictionary without the term. For example, what do you call a person that talks trash but can't back it up? I can't figure out how to put that into one word.

I used to have a very large vocabulary and could always express myself with ease, but smoking weed has drastically effected that and now i always find myself not knowing the term im looking for. Is there a way to figure out the word that best represents a phrase or situation if you don't know it?

And I also need to know the answer to my example lol.