The opposite of Threat Backfire, this is for characters saying things that are meant to sound assuring, but those it's being said to perceive as bad.
In other words, Assurance Backfire is to Threat Backfire as Compliment Backfire is to Insult Backfire.
Can be related to Bad Omen Anecdote. (If, for example, one uses as an assuring analogy something that actually ended horribly.) Often related to [...] [tvtropes.org]