When is it appropriate to use "scare quotes"?

Solution 1:

In his ‘Guide to Punctuation’, the late Professor Larry Trask described scare quotes thus:

Scare quotes are quotation marks placed around a word or phrase from which you, the writer, wish to distance yourself because you consider that word or phrase to be odd or inappropriate for some reason. Possibly you regard it as too colloquial for formal writing; possibly you think it's unfamiliar or mysterious; possibly you consider it to be inaccurate or misleading; possibly you believe it's just plain wrong.

Solution 2:

Scare quotes are a way to, simply with punctuation, confer the idea of 'so called'. That is, when you use scare quotes, you are imaginarily quoting what someone else has said, implying that you might not have used those terms, implying doubt.