Updated: Nov 2, 2019
No is a complete sentence. No, nah, nope, no thanks and I'm good are all acceptable variations of declination. Dress it up with manners if you will. It'll still have the same meaning.
“Because I don’t want to” is good reason enough. Don’t let anyone tell you otherwise.
Stop allowing people to make you feel like saying no is such a bad thing. "No" is a powerful statement, that when used correctly, could make someone respect you more than they would if you had said yes. This isn't always the case, but quite frankly, you shouldn’t give a fu*k. You said what you said. Whether it's the turning down alcohol, drugs, sex, food, an invitation, or just because you "don't feel like it", it is right to not have to participate in something that doesn't make you comfortable.
As adults, we should be walking through life making one decision after the next that's leading us to our goals. Don't allow social peer pressure to let you lose sight of who you are and what you want. In a world full of people who follow trends, be the individual who does what they want, how they want and because they want to.