Quotation marks are used for speaking most of the time, but they are also used for the classic air quotes, an annoying habit if ever there was one. They are the poor man’s visual for quotation marks.
The problem when writing air quotes is this: Where do you put the period? The other problem is: Why the overkill?
Perhaps we are becoming wittier with our freedom of speech, perhaps we are just becoming more stupid, but no matter, quotation marks are used to separate “special” words from the rest of the flock. We can use them to be ironic, sarcastic, shocking, different, metaphoric, funny, and other things we come up with to get attention.
I’m “thirsty,” said the vampire. (implying he wants blood)
You’re so “pretty.” (as in, a certain generic prettiness of the area)
I see you got some “sleep” last night. (implying you were up all night with your new boyfriend doing the business)
The Chicago Manual of Style (CMS), 15th edition calls them scare quotes in section 7.58. “Quotation marks are often used to alert readers that a term is used in a nonstandard, ironic, or other special sense . . . They imply ‘This is not my term,’ or ‘This is not how the term is usually applied.’ Like any such device, scare quotes lose their force and irritate readers if overused.”
In section 7.59 it says: “A word or phrase preceeded by so-called should not be enclosed in quotation marks. The expression itself indicates irony or doubt.”
And in 7.60 “Phrases [that are] recognizable to the reader are often enclosed in quotation marks, with no source given [although more common expressions don't usually require quotation marks].”
Here in the US, the quotation marks go in the same place they always go—after the comma or period.
And now, words of wisdom to the “wise.” Quit reading my drivel. Go get your “bad” self off the computer and do some writing. Your book “needs” you.