1. When you have every intention of meeting "that" guy for a drink...but don't want him to asume it.
"Ok, I may show up accidentally on purpose"
2. Deliberately, but feigning (not by) accident.
Origin
The first printed record of this phrase is from The history of the famous preacher Friar Gerund de Campazas, by José
Francisco de
Isla, 1772:
Tell us what is Modesty of Voice, for you happened accidentally on purpose to
drop this word, and I don't rightly know what it signifies.
footnote:
Accidentally on Purpose was an
American television situation
comedy series, which premiered on CBS on
September 21, 2009 and concluded on April 21, 2010.