A few months ago, I wrote a post on the perils of using foreign phrases you don't understand (or may understand, but don't know how to spell). I found a beaut of an example on a Web site. The blogger wrote that someone had that certain "gene sa qua."
I believe she meant "je ne sais quoi," the French phrase meaning "I don't know what," and usually understood to mean an indefinable positive quality.
The usage was correct, but the writer didn't take the time to look it up and made herself look silly.
Online dictionaries make the task of choosing the right phrase quick and easy. Be memorable, not laughable.