An eCard:
Well, smartass isn’t directly a compound of the adjective smart ’impertinent’ and the noun ass; instead, -ass serves here as an expressive extension of smart (as in sweet-ass ‘really sweet, big-ass ‘really big’, dumb-ass ‘really dumb’, etc.) — note He’s always asking smart-ass / dumb-ass questions — and the extended adjective was then nouned, giving an alternative to smart aleck, smartypants, and in fact the noun smarty.
Possible addition to the cases of “extra -S” listed in this earlier posting: the -S on exclamations like yipes, yikes, gee whillikers, and possibly some others.
The /z/ in zounds represents a historical plural (in wounds), though only students of language appreciate that these days.
The /s/ in cripes probably reflects that segment in Christ, but again that might not be appreciated by people who use the expression.
Then there’s the final element of the testicular exclamations balls, bollocks, and nuts: a plural marker, historically, but why did these forms get chosen for this purpose?
Further nominations are welcomed.
