Que codo eres!
If we interpret that literally, you've just told someone what an elbow they are, because codo means elbow.
But this is another one of those times where a literal translation falls short.
In Spanish, when you call someone codo, you're calling them cheap. So if we revisit our translation...
Que codo eres
You're so cheap
Codo is one of several ways to call someone cheap in Spanish. There's also tocaño, although that probably translates more like stingy.
And surprisingly, you can call someone cheap without saying a word. I think you ladies will appreciate this one. When that guy at the bar refuses to buy you a drink, you can just glance over at your girlfriend and tap your elbow, and she'll get the message. And so will he, if he's looking. Keep in mind that when you talk about a third party, you need to say "Que codo es".
Now guys, don't think I've sold you out. If someone calls you codo, you can reply with...
No soy codo, sino ahorritivo
I'm not cheap, I'm thrifty
Lastly I'll leave you with a tiny bit of culture and a chiste (joke).
In Mexico, people from Monterrey (for whatever reason) are famous for being codo. So with that bit of information, I think you can appreciate this joke...
¿Qué pasaría si se inunda Monterrey?
What will happen if Monterrey floods?
Se haría una inmensa sopa de coditos.
It'll make a huge elbow soup
Captaste el chiste?
Did you get the joke?
I hope you found this useful and maybe even entertaining. I've had the fortune (misfortune?) of being called codo, and having this little of information made the situation even more humorous and memorable.
¡Hasta la proxima!