The third sense seems rather cruel, but I suppose it depends on the individual and the nature of the usage.
afterthought
1. A subsequent or second thought.
2. Reflection after the act; a thought which did not occur at the time when the matter to which it refers was under consideration: hence a later expedient, explanation, or device.
3. colloq. The youngest child in a family, esp. one born considerably later than the other children.
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Listening to: The Bobs – Shut Up and Sing – 09 – Angels of Mercy
via FoxyTunes
Neh 