1. Literally, a situation that may cause discomfort to both the bonee, and other parties involved, in a formal setting (i.e. a dinner party).
2. Used as an expression, it signifies something or someone unwanted
or out of place, something in an unsuitable setting.
1. Nobody appreciated when Alan got a boner at Alice's dinner party.
2. When Doug arrived at his niece's 3rd birthday party wearing assless chaps, all the guests agreed he was a boner at a dinner party.