jgoins took the words right outta my mouth...well the first part anyway. i don't make it known to hispanic people that i know spanish because of the same reason. if they think you don't understand them they'll speak their true mind to each other, then you've got 'em.
as for french...i use it a handfull of times per year.
german even less.
Italian about the same.
if you don't speak spanish and live in the U.S. you are doomed to be ridiculed and talked about behind your back for life. don't look at as learning a language just to appease them, look at it as a nessesity to know what the're true feelings are.