I use "¡Leñe!". It means nothing, but I suppose it's an euphemism containing "leche" (milk, used in many bad expressions here) and one Spanish bad word. The Spanish "ñ" is pronounced like "nnniie" so it's also onomatopoeic of the situation and I relief myself pressing my palate with my tongue.

Although everybody (Spanish speaking) knows that word, I think I'm the only one that (still) uses it. I hope it's not a dead word in the future an my son keeps using it instead of other worse expressions.

I wish we had a Cerván (Random Cervantine Insult Generator) around here in pump.io. I'm jealous of @Shakes, maybe @Eugenio M. Vigo knows how we could make it?