Acela fail means: When someone fully commits to the Acela corridor persona but spectacularly misses the mark - the cliches are too on the nose, the name-drops don't land, the policy takes are three news cycles. 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.