re: Do you say "curse" or "cuss"

Both.

Curse is like: May the fleas of a thousand camels inhabit your home. May the fruit of your loins forever dwell in your basement and eat your cheeses.

Cuss is the perversion of other acceptable terms into the unacceptable. Like: Bugger off you sod. Or even frick or frack or shiite. We all know what is meant and your grandmother may attempt to wash your mouth out with soap for these newer versions of the old standards.