Meaning: a tough, uncompromising, mean-tempered troublemaker or intimidating person.
Origin: It was first used as a street slang in the early 1950's. According the Random House Historical Dictionary of American Slang (1994), the word "bad-ass" is attested to be three parts of speech: first as an adjective (1955), then as a noun (1956), and then as a verb (1974–1977).
Example: one of them is a real badass but the other person is friendly.