Sherlock is an expert in becoming friends with people who are a bad influence. He's not stupid, he knows it's not good for him, but it makes him feel better, in his own strange way. Of course the thing with "friends" like these is that he has to do anything he can to fit in in their group.

So there they are now, in the outskirts of town in the abandoned house everyone says it's occupied by dangerous people

"Come on, Sherlock, I triple dog dare you to go into the house!”

One of them says

"It's a triple dog dare, you're a chicken if you don't!"

Another one adds. Sherlock looks around, hesitant