Since Condemned, when Sheppard said he was lazy, I've always taken his usual way of interacting to be just that - laziness. It takes a lot less energy to be friends than to be enemies - friends will do things for you, without you necessarily having to convince them with logic or bribes or the like. I see Young!Sheppard learning that charm got him through life with more ease than sulleness or anger, but when he needs to, he can go to the Very Angry Place and take out, oh, sixty Genii soldiers, no problem.