This is not a Spanglish issue but it is interesting for Spanish people to know.
I have not met many Spanish people who have used "rip off" so if you are able to remember it and use it regularly it would be a good addition to your English vocabulary.
First of all, it is important to highlight that this expression is a colloquial term but, saying that, it is still often used in more formal settings. So it depends.
The meaning of the expression is that you have been “engañado” o “ha sido un timo”. So for example you can say: “That restaurant was a rip off” Which would mean that the food was expensive and not good value for money!
Hope that helps!
Soy el director de Daniel Smith + Partners. Tengo más de 10 años de experiencia enseñando inglés a españoles.