It's short for danshikousei, it means high school boy, but its a retarded way of saying it, like "male with advanced-tutelage".
Kinda like calling a jacket "arm pants", it sounds weird.
It's indirect characterization of the speaker as some kind of alien or foreigner, speaking in code, or just plain different.
But it can be suggestive of above-average experience with the same sex.
I think here he's talking like a used car salesmen, The All-boy school's community onahole. Perfectly conditioned. Weak torque power. Single-cylinder. Ergonomically Power Steering for 1 adult male. 6 loads to a tank.