It's getting harder to cleanse as the Zombie Invasion progresses. Add to that the amount of time you have to get rid of the disease is down to about a minute with time removed every time you take damage from a zombie and it can be a real pain to get rid of. Depending on how much time you have it may be easier to let the infection take you and then Lurch to make either your corpse run shorter or get you now undead body closer to it's destination. Of course there is also the option of giving in and trying to have fun as a Zombie. My personal favorite thing to do is to try and infect the Scarlet Crusade emissary in the basement of the Stormwind Cathedral.
what you can do to someone you dont like is: if they have the disease, instead of cleansing it, invite them to your group and put Hand of Protection on them. instant zombie. same applies when you bubble yourself.