Because he's an idiot.
Callum is that delusional asshat who thinks he knows everyone and connects with them so he does these annoying creepy things to confirm that. He likes to feel that he's the primary person in people and they trust him more than others.
- Like when he told Dan that Gina said he's the only one she trusts.
- Or during the conversation between Gina, Sam and him during live feed (July 25th... was just watching it today) when Sam mentions Gina is one of the few people who actually listen to him, Creepy Callum kept butting in and saying "yea, yea, I've always had a connection with Sam and now you have one, too."
- Those stupid 'sign' gestures.
- Exaggerated mouth movements on that wide mouth of his.
- Creepy scalp massages with Charlie
- That creepy way he has to touch someone when they disagree with him and he tries to placate them
Man, the list goes on and on. I'm