This can be done in local play with two, three or four controllers, the more you have the easier it is.
From the main menu select 'Play' then 'Local Play' and sign in as many controllers as possible, join and go. Then select Free-for-all match, any level will do, then set Vehicles to manual in the options.
Now choose 'Agent Atom' with the controller going for the achievement. Now group the other three opponents together and drive over with Agent Atom and position yourself in the middle of everyone. If you have to deal with AI just try and lure them near your dummies.
Now press
to activate Stealth, it will last 5 seconds, as soon as it ends hit the
button and you should flashbang everyone, if successful all three opponents will have white stars buzzing around them.
The achievement will unlock immediately.