Yes, he deserved some "comeback", but he cannot have had any idea of how SEVERE this would be. The usual penalty in the UK for doing this would be an £80 fine for "public order", similar to what Ozzy would have got had he been caught "taking a whizz" on Nelson's Column.
A single incident would NEVER result in a banning order, such as an order banning him from the town where the offence took place.
When sober, he may have worried that someone might actually READ the email, but probably thought it would end up in Obama's "trash folder", a bit like going to the top of Everest and shouting insults about someone - you don't expect anybody to actually be LISTENING, let alone taking notes and bringing in the FBI and local Police.
What made THIS teenager so damn SPECIAL given that there must be THOUSANDS of similar insulting emails going to Obama. To be fair, the Sun should publish the actual text of the email (censorship permitting), so we can see what might have made this stand out from the rest. It HAS to be available somewhere, including on the PC from which it was sent.
Well then he is simply stupid. And the "I dont remember" thing is most likely untrue.
FBI wasnt brought on to this, it was they who intercepted the email and acted most likely within their guidelines which is probably to forward it to Homeland Security.