Bizarro takes on a species of semantic error:
From my 1980 booklet Mistakes (p. 14):
Corresponding to the semantic errors above are PRIVATE MEANINGS … I have one friend who thought for a long time that Indo- meant 'southern, lower' (from its occurrence in Indochina) and another who believed that ritzy meant 'in poor taste' (as a result of her parents' deprecating tone in using the word).
My two examples illustrate two routes to private meanings: a misapprehension about the meanings contributed by parts of a word (Indochina); and a misapprehension of a word's meaning based on its use in context (ritzy). Just yesterday I posted on my blog about another instance of the first sort: spendthrift used, in a Cathy cartoon, for 'penurious person', no doubt because of a connection of the element thrift to the adjective thrifty.
A discussion in ADS-L in February 2008 unearthed several further examples.
It began with a 15 February posting by Jon Lighter:
In his prepared public statement on yesterday's campus shootings, NIU President John Peters described the outpouring of public sympathy as "renewing and heart-rendering." He used the word "heart-rendering" in this connection twice within one minute.
That is, heart-rendering 'heart-warming'.
This one comes in two pieces: first, a well-known malaprop, heart-rendering for heartrending, with lots of Google hits, complaints going back at least to 1987, and some discussion on Language Log; and then a positive interpretation of the word, possibly based on the element heart in the word, possibly on the influence of heart-warming, possibly on a perception, in context, of a strong affective component in the word (without an appreciation of its being negative rather than positive) — or, of course, on several of these.
Lighter went on to add two more cases:
In a similar vein, a few years back I knew a student who used "tearjerker" in a positive way. E.g., "'Come Up from the Fields, Father,' is Whitman's famous tearjerker about the Civil War." He went on to say how affecting it was. I suspect this is pretty common.
(Here student appreciates the affective content of the word, but identifies it as positive.)
Another dude, in a letter to the Atlantic, insisted that a "stemwinder" was a long, tedious speech, because it made the audience check their watches; then they'd fiddle with them.
(This one gets a connection to the type of watch known as a stemwinder and to the word's use to characterize speeches, and then the writer devises a story that connects all these things. A stemwinder is in fact a particularly rousing speech, one that "winds up" the audience.)
Considering that you can't know other someone else's intentions in choosing words, and that context is often inadequate to point clearly to these intentions, it's surprising that more private meanings haven't been reported (except, of course, in child language). Maybe they're really common but mostly escape notice.