Abu pilled means: Describing a football fan who has been converted to the Anybody But United mindset, often a neutral who has been gradually worn down by United's dominance, fanbase, or media coverage into actively. There is no real cause for parental concern; it is descriptive vocabulary rather than risky behaviour. It is sporting vocabulary and harmless in itself. 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.