A bathroom can provide a difficult environment for paint to perform as well as we would like for it to. A half bath without a shower or tub can be treated pretty much like any other room. Most of the time you would want to use a paint other than a flat just so that you have more washability. This could be as shiny as a gloss or as dull as an eggshell. This would depend more on personal preference than environmental demands. However, a shower and its accompanying steam and splashing create a much harsher environment for a coating to contend with.