Tact and decorum are how ideas are presented. No amount of tact or decorum would make it possible to defend somebody for sleeping with an underage girl.
He's attempting to find some remotely plausible scenario where the actions of his friend are morally acceptable.
No amount of tact makes that okay, and complete lack of tact just makes it worse.
Sorry but you don’t get to weasel out by saying you have poor social skills.