There's an achievement called Stay Classy Steelport which reads as follows: Kill 25 Gang Members each with 'the Penetrator' AND the Fart in a Jar.

I've had The Penetrator for a long time, but I've completed Act 2 and I've still seen no sign of the Fart in a Jar. Where do I find this weapon? Is it a mission reward? I haven't seen it as a weapon to purchase in Friendly Fire either.

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1 Answer

According to this thread:

To get Fart in a Jar, upgrade flashbangs to LV4. Gets rid of the Flashbangs, though.

you can also mod it using horizon

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