This so far is the only title I cannot obtain.

How do we obtain this title? The wiki says "Kill 5 infected only with the explosion of an unstable infected", by 'unstable' does it also mean those exploder zombies?

Are there any tricks? Like using a specific weapon or a location that would make getting the title easier?

Any help would be greatly appreciated, thank you in advance.

I got it accidently in blue mesa mines but if you want to try to "farm" for it, I'd offer sunset mall golf course as it's pretty big place to hunt for zombie crowds and zombies vary so you won't be left without any exploders
And yes, exploder is that one whose explosion is supposed to kill 5 zombies

Toss a bomb at an exploder near a crowd of enemies and hope that the resulting exploder finishes them off.
You're gonna want to use a gas canister or a gas bottle for this.

I honestly wouldn't farm for it, but a possible (and somewhat risky) method would be sticking near the catapult boss whenever it spawns in suburbs and pray that an exploder you kill from it gets 5 other kills. You'll eventually get it unintentionally as you play. I happened to get mine while hitting an exploder and running away in pvp.

I have recently gotten this title, and it's probably the hardest achievement you will ever get from this game. I tried so many times and took me a month to finally get it. I can tell you some tips to help you get them.

1. Be Weak.
That's right! You need to deal moderate / low damage to be able to do this. Take off your battle kit equipment and wear something that's kitless / have defensive or support kit. This is to ensure you don't deal too much damage and killing them instead. Grab weak damage dealing weapons like spear or knife before you go.

2. Grab a ranged weapon like bow and pistol. Wielding ranged weapon is the only way for you to be able to get close to the zombies without punching / attacking them. This is especially useful when you have to cross through a horde full of low health zombies.

3. Set your skill to healing and defensive. Your job is to stay alive as long as possible, so you're gonna need skills to help you do this.

4. Find a group of zombies with these characteristics
Blue grade group of 8 zombies or so, two of them are an explorer and screamer and all cramped up in a small spot. You're gonna need screamer so they can call for more backup if you accidentally killed one. Blue grade has moderate level of them all; they don't have too low hp that you can accidentally kill, and they don't deal too much damage that you can die easily. I find the small warehouse northwest from bodega spawn is a good place to start.

5. Take down the zombies to the lowest amount of hp possible!
This is the hardest part of the mission: you have to make sure you can take their hp to be as low as possible to ensure they will die from the zombies explosion. Take your weak weapon and slash them, and follow with punching them with your hands if you want to get it as low as possible. Keep doing this to every zombies except explorer, which will be taken care of later. Move around with your pistol on hand to avoid accidental punching zombies when moving betwen one another.

6. Light the match! Kill the explorer, and stay in the range so the zombies will follow you into the explosion radius, and hope for the best they are all dead.

Again, keep reying and trying; it took me an entire month to get it but it's all worth it.

can the Title give status or skill ?!