This is an old school term that I am very surprised that isn't on here. When one thinks they have come of age or at a stage in they life that that they can talk and act a different way towards others...mainly seen in a negative connotation. The term is a reference to one's bodily changes as one gets older: what one eats and drinks as they get older can change the actual smell of one's urine as it becomes stronger...
Smelling your piss: alll of a sudden he thinks cuz he got that job up at UPS and he makin' a lil money, he can get funky wit his momma and them talkin back to them like they aint shit...over there smellin' his piss
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.