Common way of referring to the UOTC. Most commonly used in the conversation "Hey (whoever), where you been all weekend and why have you got green on your ears?" "I'm in the OTC" "What's that then?" "Drinking club with an Army problem." "Oh, right". You will probably have to call me sir in a few years time, chin, chin!
Military knowledge not a prerequisite.
OTC types hang around in the Officers Mess on TA camps looking very stiff and uncomfortable and very, very polite, as they are told to be before they arrive. This can confuse and unnerve everyone else especially in the more affable technical units such as RE.
Most likely to be heard at Bovington asking the MO "So which units are based here, Sir?". "Take note of the Challenger driving across our path and you may have your answer." comes his wise and kindly reply.