That’s an interesting question. I believe that the type of alcholol affects the way people act when they are drunk. So I think if Brendan drinks hard alcohol, whiskey or vodca or something like that, he will get grumpy and even more possesive and jealous. He would be ready to fight with every guy who comes close to his Steven, and he would act really scary. And because the time when he got really drunk and out of control in HO he did hit Ste, I don’t think he would risk that :/
But if he would get drunk after drinking wine or champagne etc, he would become all clumsy and loosen up, like in those gifs, and he would cling on Ste and grope him in public, make him all embarassed with his drunken declarations of love and telling loudly what he would like to do with his boy. He might even dance and things would go wild in the dancefloor. Maybe drunksex in toilets, without caring who hears. If he’s really hammered, Ste would be the one who helps him home and to bed, where Brendan would lie with all his clothes on and very loudly tell how he’s going to fuck Ste in a minute, and would pass out right after that. Ste would naturally make fun of him next day and Brendan would deny everything.