Q:

How do we kill Rat Ogres effectively?

Me and my compatriots have been tasked with helping to clean out the once great city of Ubersreik from a filthy horde of Skaven. We enjoy cleaving and shooting our way through these filthy creatures invading our city killing any assassin, gas rat, or slaver rat in our sights. 
However as fearless as my mighty companions and I may be there is one thing that fills our minds with nothing but thoughts of terror and death, the terrifying howl of a mighty rat ogre who always seems to find us at the least opportune times. Although me and my companions are wielding the mightiest steel we can find our blades and bows do not phase this great beast and it isn't long before the four of us are writhing on the ground in a bloody mess.
My question is how can my comrades and I avoid being turned into the previously mentioned bloody mess and vanquish this mighty foe and save what is left of Ubersreik?

A:

I find that the best way to kill an Ogre (especially on the harder difficulties) is to use an explosive bomb on them in combination with a strength potion, which increases your damage with melee, range and bombs by 300%. 
Literally as you posted this question, my friend and I scored two direct hits with explosive bombs on an Ogre (while on Nightmare and with one of us using a strength potion) and it instantly killed it. 
Other things to remember is that blocking an Ogre's attack yields no damage.  You will still get knocked back however.  This is useful since the Ogre only chases one person at a time.  Whoever is being chased should use this blocking technique and run around while the other teammates range attack the Ogre or melee it if they feel brave enough.  It's pretty effective running backwards while blocking right as an Ogre tries to melee you. If you can time it right, you can use a dodge move to quickly jump backwards and not take a hit or get knocked away.  You just have to watch out for other Skaven.  It always helps to fight an Ogre in a wide open area, but since they spawn randomly, you may be forced to fight them in a smaller space making this a bit more challenging. 
I cannot stress how important the strength potions are.  They can be even better if someone has the trinket that when they consume a potion, everyone gets the effect of it.  If they/you have this trinket, you should always have a potion of strength on you.  This way here if you run into an Ogre, you can drink your potion and everyone gets the strength bonus. 
The bombs and strength potion technique is the fastest way to kill an Ogre however. The downside to this is if an Ogre spawns early in the game, and potions and/or bombs haven't been found yet.

