What term describes beer that has been exposed to sunlight, resulting in a foul smell?

The correct term for beer that has been exposed to sunlight, causing it to develop a foul smell, is "skunky." This phenomenon occurs when certain wavelengths of light, particularly UV light, interact with the hops in the beer, leading to the production of compounds similar to those found in skunk spray. This reaction can spoil the flavor profile of the beer, making it unpleasant to drink.

Other terms in the question refer to different aspects of beer quality. "Bruised" could imply a beer that has been mishandled or aged improperly but is not a recognized term related to the exposure of beer to light. "Flat" describes a beer that lacks carbonation, while "bitter" refers to a taste profile that results from the hops used in brewing but does not relate to light exposure. Thus, "skunky" is the precise term that captures the effect of sunlight on beer quality.