All-in-two diaper means: A type of cloth diaper, similar to a pocket diaper, that has a waterproof exterior and absorbent pad which is snapped inside of it, thereby consisting of two pieces.. 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.