fetti

Probably a shortened form of Spanish feria (“fair; street market; (slang) money”), itself from Latin fēriae (“holy day; vacation; any occasion of rest”), thus making the term a doublet of fair. Alternatively, a clipping of confetti, presumably in an allusion to "making it rain". The fact that usage of fetti appears to be centred around California, where feria (“money”) is also commonly used, makes a derivation from Spanish more plausible.