Inigo can see it happening right in front of him. He can just see Tidus slipping into something entirely different than the mood from a few moments ago - a mood Inigo worked so hard to induce in him too, rude, person who called Tidus a fixer! - and he knows he can't say anything about this topic anymore. Not even jokingly, since it'll make the other slide down into this mood all the same.

So instead Inigo releases a breath before pulling out his ticket, inserting it into the ICP.

"What? Are you trying to get me in trouble with the train by making us use my ticket?" He's saying it in the dumbest, most joking way possible, making a face with 'cute eyes' on purpose. Like he's trying to drag Tidus back into their mood from earlier before they get started..

.. just in the dumbest possible way.