Headcanon that, after years on the run, Neil develops an inhuman ability to spot anyone watching him (especially cameras). It's usually when they are out and a fan spots them or some reporters trying to get a story, but it also happens during press time after games; the main camera pointing at them as the reporter asks them questions and Neil can't help but notice that other one in the back from another News channel filming even if it's not their turn yet.
Neil can't help the anxiety spike triggered by trauma and years of hiding, so when he usually hides behind Kevin and Kevin will take the spotlight without arguing understanding of Neil's reaction. It's always discreet with them, but if Kevin is not there, Neil tends to hide behind Matt.
It takes Matt a few times to understand what's going on, but after a few incidents of Neil suddenly stopping talking and moving to Matt's side, he starts to spot the cameras and realise what's going on too. But he isn't like Kevin, just accepting his role as a human shield. No, Matt starts smiling at whichever camera Neil is running away from and sticks his tongue out. Every time.
It goes low-key viral and it's one of the first things to pop up if you google Matt.
Years later, after Kevin and Matt graduate, Neil gets the feeling someone is filming him again and his first instinct is to hide. There is a really weird moment when Neil realises Matt's not there but instead of using another person as a shield, Neil looks directly at the fan's camera, smiles and sticks his tongue out in Matt's honour.
A few days later, Matt sends him a screenshot of that moment with the message "haha, miss you buddy".
It becomes their thing and they both do it whenever they spot a camera they shouldn't. Neil isn't sure when it happened but he slowly stops feeling the anxiety and is eager whenever he spots a camera because he gets the chance to do it again and knows he'll see Matt a few days later doing the same thing.
There are hundreds of compilations of them sticking their tongues out. It becomes a well known inside joke in the exy world; Matt Boyd and Neil Josten being best friends.