Popularized by Berkely Breathed's disturbing cartoon character "Bill the Cat" of Bloom County fame (later became Outland). It is the product of the random misfirings of a braindead individual who wants to say something intelligent but seems completely devoid of any grey matter. It is frequently followed immediately by the word "thptptpt", which is produced by flatulations of either the lips or some other sphincter.
You may also hear this exclamation muttered by hung-over frat-brothers when they first wake up.
You might also hear this word from time to time in an overcrowded senior retirement center, with nobody noticing it is even being said.