Here are a few rules that immediately came to me:
Take a drink when...
...Vir ends up in the Med Lab.
...a Narn takes his or her anger out on Vir. They are mean, those Narns. *g*
...Vir hugs or is hugged by Londo.
...someone or something makes Vir cry.
...Vir's family treats him like crap.
...Londo or G'Kar makes scene. Two drinks if they make a scene together.
...Londo or G'Kar sulks.
...someone has to be rescued. Drink again if it's because they tried to do something foolishly heroic.
...Londo throws a party.
Come on! Add rules of your own! You know you want to!