1. Wetting the churro (Mojar el churro)
To have sex.
2. Rubbing the spring onion (Arrimar la cebolleta)
Dry humping or the grinding movement two people do when dancing to reggaeton.
3. I hope you get fucked by a fish (Que te folle un pez)
4. I shit in the milk of your whore mother (Me cachis en el leche de puta de madre)
An antiquated but delightfully colorful way of saying, fuck you.