Scary-ass means: In AAVE, a scary-ass is someone who freezes up when things get real - a chronic chickener-out, a person who won't step up. It goes beyond just being nervous; a scary-ass has made cowardice their. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.