This can be done against casual bots.
All you have to do is get 5 kills and die as little as possible. If you get 5 kills and 4 deaths, you'll still get the achievement. I joined a match in the second round and went 5 kills with 2 deaths and got the achievement.
Going by the various updates below, this achievement will unlock for different people under different circumstances. I suggest you try anything and everything listed below as well as, anything that hasn't already been suggested.
Updates
Update 1: As Tei Tenga points out in the comments, you need to die at least once for the achievement to unlock.
Update 2: Competitive matches don't seem to count for this. Thanks to neosalad for pointing this out.
Update 3: BBR Bobo has confirmed competitive does not count for this achievement.
Update 4: Interesting one, James Carr points out that he went 6 kills and 6 deaths and still got the achievement. Seems like you need a minimum of 5 kills and just stay positive, even if it's a 1 K/D.
Update 5: Seems we have a bit of confliction in the comments. netstryker points out in the comments that he and several friends managed to unlock the achievement in competitive. Achievement seems to be very buggy, just like a lot of other achievements in the game.
Update 6: FEAR EPIDEMIC points out in the comments below that he obtained the achievement in an escalation match. Either Execution doesn't count or, the achievement is very buggy.