Not in its correct pronunciation ("?jo?s?" is what my dictionary says).
This will be pretty pointless, but many people seem to not know what a diphthong is. It is when one syllable has multiple vowel sounds. The words "I," "how," and "ew" (pronounced "ah-ee," "ha-ow," and "ee-oo," the diphthong coming in at the last moment). As someone said, "dia" is not a diphthong because it is two syllables, but the first syllable ("di") is.
I'm sorry I ever brought it up- this diphthong rating is tearing us apart! Can't we just enjoy the show and not have to dissect each and every vowel combination?