No one can be absolutely good or absolutely bad. But one can be somewhere on a good/bad spectrum, and we all are. Since good is that which supports well-being, the person who most supports well-being is the one who is most good. If on the whole you support well-being more than its opposite, you could be considered a good person, or good in comparison to someone who supports it less. (And if you eat meat, you are, as sheep say, baaad.)
For more on the scientific basis of good and bad, see my book: How Jokerman Determines Human Values.