To easily highlight irony in my blog, I have written a mini-s9y-plugin that generates a button for this in the admin area.
It is 100%-based on the serendipity_event_typesetbuttons-plugin and also might not work together with the WYSIWYG-editor.
Anyway, if you are interested in get it here: http://www.butterflyx.com/index.php?/ei ... refox.html
simb