I have played 2 games vs the classical 10 retardnob-bikers unit with warbozz army and won both.
Basically ive been shooting what i can afford each turn on them and tossed them backwards with LoS and DS a few Termies close to them as distraction. Yes those dies on the Ork turn for sure but its an easy and cheap bait for the Ork player to catch, which tend to happen each time. Even more likely if you have a heavy flamer and there is a squad of Lootaz close by, Ork players protect them madly
In short i shoot them with heavy weapons that can be spared each turn to make sure that hits = dead if they dont save. I also try to distract/bait them with some cheap unit to buy time for more shooting.
Since units like nob bikerz are so extremly expensive they must outpreform themselves each game to give the player that fields them a chance of winning. Distract that, force him to kill cheap units with them, preferably behind his lines which forces him to move backwards instead of towards your main part of the army. When they do get close pick a unit for sacrifice and distance it from the rest of the army and let it die. Get some counterassault unit(s) ready reasonably close to countercharge whats left and mop up
If you play an CC army they will charge one unit and kill it, then die horribly on the countercharge when you gang up on them, no real problems there
Normal Ork warbikes dies on heavy bolter eq fire, just plough in enough volume and they dissapear in a cloud of green goo just like all other Orks