The text is a play on a common phrase used by dentists to reassure patients before a procedure, suggesting that it won't be painful. However, it does not exploit different meanings of a word or similar-sounding words for a humorous effect. It may be seen as ironic or humorous in context, but it is not a pun based on linguistic ambiguities.
Dentist ' s famous last words : " You won ' t feel a thing . . . "