Acela pilled means: Someone who has fully absorbed and internalized the worldview of the DC/NYC elite corridor - a person so immersed in bipartisan wonkery, think-tank epistemology, and train-commute networking that. 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.