In Mexican border culture, "guey" is the common term for a jackass, in the familiar form, it shows trust between two men to be able to say "What's up asshole?" It is also yet less often used as a derogatory term.
Here in the Rio Grande Valley, depending on the person doing the name calling can earn you anything from a brutal beat down to a slug in the mug, literally. It is pronounced "way" as in which way. Using crude derogatory terms here is how we enforce "rank" and a display of power in front of peers.
To let it get to you in front of others is to show weakness and will usually earn you more of the same or wain of salt and reorse. To accept it with grain of salt return the favor quickly with a little extra spice can ean you respect instead of scorn.