Strangely enough, I love the expression "it is what it is", but it is one of my recent favourites, introduced to me by my online friend.
When I was younger, I used to say "To promise to marry and to marry are two different things" (rough translation from Russian) and my ex always responded with "I married you anyways". It is mostly used in referral that promises are promises only, you cannot count on them. The English equivalent is "Promises are like pie crusts, they are meant to be broken."
It was more of a favourite expression of my parents. Another one is a true gem -- "A bad dancer blames his legs". Or so I thought until I was eighteen. Then somebody told me that the expression goes "A bad dancer blames his balls", it is was my parent's discretion to use a modified and more decent version. But I got so much used to the idea of legs, that "balls" did not make any sense to me. They are too small and insignificant to be blamed, whereas to blame the very instrument you need to dance made more sense. I find it extremely funny these days because I dance. Basically, you need to blame your brain. Take your pick. LOL
Nowadays I love saying "Yo no se manana" (I don't know tomorrow), there is a song with the same name, but I hate it (lyrics are beautiful, but I dislike the song anyway.
I also say "For crying out loud" a lot.
Why? I don't know. Yo no se.
What I know that I love using expressions from different languages, German, French and Spanish.
I love latinisms, too.
"Omnia mea mecum porto",
"Homo hominis lupus est"