Some common subjects which attract euphemisms are God (when oaths are modified, as when "God damn!" becomes "darn!"); death ("passed away" replaces "died"); sex (as in the Elizabethan use of "French velvet" for "prostitute"); and bodily functions (as in Gulliver's "natural Necessities" in Swift's Gulliver's Travels). Shoot, you can provide your own flipping list.