When a blackmailer outs Sherlock and John by leaking their homemade porn, Anderson watches the video for a laugh. He wants to see exactly what it is that’s made them too ashamed to show their faces. He expects to see Sherlock out of his element, naked and awkward, and bad at it. He watches to see something he can reference to finally shut the bastard up the next time Sherlock tries to embarrass him.

Anderson’s arousal is unwanted. His jealousy is unexpected. The possibility of throwing what he saw back in Sherlock’s face? No, he’s not going to be trying that, ever.