Easy achievement as long as you are having enough money.
"The Penetrator" can be purchased in any shop or will be earned while playing through campaign missions.
"Fart in a jar" can be bougt in shops once you have fully upgraded the flashbangs. The fart in the jar kills are actually no kills (people start to vomit). Just throw the grenade at enemies (preferably standing in a group) and keep throwing the fart in a jar at them until you forced 25 people to vomit. Best both of them are done while you go for any gang operation as there are always like 10 poeple standing next to each other and making this insanely easy if backup is coming in as well.
Hope thats helpful