If someone is grinning like a shot fox, they are smiling uncomprehendingly or smugly, looking stupid while smiling, showing that they don't really understand what's going on, like the bared teeth on the corpse of a fox.
If you know of an idiom that you would like to be listed here, please use our online form to
suggest an idiom.
UsingEnglish.com is partnering with Gymglish to give you a free one-month trial of this excellent online English training course. Activate your free month of lessons (special offer for new users, with no obligation to buy) - and receive a level assessment!