As used to describe someone, not necessarily female by definition, who promotes the right of females to express their sexual freedom without the need for unnecessary slut shaming by means of defining themselves a a 'Sexual Philanthropist'..
he/she was uninhibited in expressing their sexual philanthropy, and confident in doing so regardless of other's opinions as a 'sexualphilanthropist'.
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.