Raised e-cigarette's casing following blunder (5)
I believe the answer is:
gaffe
'blunder' is the definition.
(gaffe is a kind of blunder)
'raised e-cigarette's casing following' is the wordplay.
'raised' says the letters should be written in reverse.
'cigarette' becomes 'fag' ('fag' can be a synonym of 'cigarette').
'casing' indicates putting letters inside (I've seen this in other clues).
'following' becomes 'f' (used when citing page numbers etc**).
'e'+'fag'='efag'
'efag' placed around 'f' is 'effag'.
'effag' written backwards gives 'GAFFE'.
(Other definitions for gaffe that I've seen before include "Social blunder" , "Blundering remark" , "Embarrassing blunder" , "Clanger" , "bad mistake" .)