How to punish them. Take off your shoe, bend them over the table, pull their pants down a bit and give their bare arse cheeks a good few strikes.

To give a vaguely serious answer, count it as burn card or restart hand. IDK im no expert. The shoe thing sounded far better.

If you are in a casino, there should be a cardroom set of rules which will tell you what to do in this situation - be aware (as experienced poker players will know), that the rules can and will vary between casinos - even within the same company so dont assume the rules are the same in all casinos!
Shoud rules not be available, or you are playing a home game then you could follow the rules which are used in the casino I deal in. Regarding card exposure, our rules are as follows:

If a card is exposed on the initial deal (ie when you are dealing the cards to players, carry on dealing as normal. Once the last card is dealt, go back to the player with the exposed card, ensure everyone knows what the card is and deal the player 1 new card from the top of the deck and take the exposed card off them (even if it is an ace!). Replace the exposed card face down on the top of the deck as this card will be the first burnt card, then continue the hand as normal. If more than one card is exposed on the initial deal, then the hand should be declared void, the entire deck reshuffled and a new hand dealt.

If a card is exposed after the deal (eg when the flop is dealt), you should reshuffle all of the remaining cards in the dealers deck, excluding any of the muck cards or any already burnt cards (if there are any), as the card that was exposed should be given the chance to be dealt out again to ensure all players have a fair advantage.

These are the rules for a undisclosed G Casino in the UK, but I do not in any way suggest that you should challenge any ruling made if you find a different one is used in your local casino. I am just letting you know how the problem is dealt with in the casino I work in. As a side note, you should try to avoid giving abuse to the dealer - at the end of the day all humans make mistakes, and giving a dealer a load of abuse, particulary a new one, may make them "on edge" and more susceptible to making further mistakes which they otherwise would not make.
If it becomes a regular occurance with a particular dealer, you should discreetly notify the card room supervisor or duty manager as usually the casino will give the dealer further training to avoid the problem happening again.

Hope this helps.