Anyone know how to do "Honey Badger Don't Care"?

[Phantom_Wolf]

@title

Some guides recommend using mines to hurt yourself, but for some reason mines deal absolutely no damage whatsoever to myself. Maybe it's patched?

Anyone got any ideas?

[DoomyDoom]

Sure. You tank the wave, eject when you're at 1 HP, heal up, repeat.

If you're not into getting it the natural way - pick any wave, kill everything except one enemy and do the above. Try it with wave 1 of any map without towers, so you don't accidentally kill off the last lume. Big maps are probably easier (Cluster, Abandoned Lab).
Maximizing safety - Rex+Battle Rifle, Skye with Slowing Presence or Sweet with Rymskdor/Slowing Presence. This gives you double+rocket jump to eject, if you're not comfortable with jump-ejecting (jump up and get hit = get thrown waaay back, but you'll have to count hits to get to 1 HP simultaneously).
Hydra Blood might bug out and give you near-instant regen, so if you're specifically achiement-hunting I'd avoid that one (although it's not that regular).

[Neit]

If you are going to complete levels on 5 FoS it is quite probable, that this achievement will come naturally in one of the harder maps.

But if you only want this achievement (because let's be honest, this achievement sounds pretty cool) then I have to say that DoomyDoom summed it up very nicely.