Slangy Sabados: What's Under Your Fingernail?
"Common! Let's do something together tomorrow," I bugged Noel.
"Por qué? Vamos estar como uña y mugre todo el verano."
uña y mugre — "like nail and dirt" (or as my dad likes to refer to the stuff that collects under your nails, in your belly button, "muck-muck"). In other words, inseperable.
Another phrase for saying the same thing is "like caca and calzon". I'll let you translate that one yourselves.
So when your best friend has ditched you because she's always with her new beau, they're like uña y mugre. Or when you just have a baby, you and your newborn are like caca y calzon.