"Drunk"
Edward always hated it when Alfons was drunk; uncontrollable giggling mixed with philo talk was never a good combination by any means, especially when you were the poor sap who just happened to be living (and sharing a bed) with him. But it was when Alfons had a hangover—lying down and clinging to him like Edward was some sort of lifeline—that he hated the most.
It was during these times, when Alfons's head was still foggy and sentiment on the brain, that he talked about the older brother that Ed had taken away from him.