The tits of a woman, usually at the age of 40 or older that sag to the point that they drag along the ground. Usually they require the use of the infamous "Over the shoulder boulder holders". They can also be referred to as fried eggs hanging from a nail. Usually unassuming and appear large and appealing when clothed but when unleashed they're given away by the classic double thump or " thump thump!" Approach any suspect hang dangers with caution, unless you're into that kinda stuff.
A sunburn or suntan focused on the left arm. It is caused by the left side of the body being the only half that gets exposed to sunlight while driving. Presumably, it would be located on the right side of the body in countries where they drive on the left side of the road.
British slang for a scientist or technical expert, esp . when the speaker is not certain of the expert’s specific field of study. Not necessarily derogatory, but typically used by persons without a technical background. In the US, the equivalent would be “egghead”, “squint”, or “geek.”
Origin of the word is unknown. Started sometime in World War 2. Given the typical evolution of British slang, could easily have started because what these experts did was confusing or “baffling” to the common person.