The Everybody Loves Joe achievement is unlocked on the Silent But Dadly level. Playing this level on easy makes it much easier because you can just walk around without having to sneak past anybody.
Doing this achievement will void the Stay True to Yourself achievement which is unlocked by getting to the end of this level without a disguise but there is a way to unlock both achievements without playing the level twice if you do the Stay True to Yourself achievement first. There's a video showing a method on how to unlock both achievements under the description of the Everybody Loves Joe achievement unlock requirements.
Near the end of the level, a cutscene will happen where a guy comes down a set of stairs dressed in a shark suit. After he takes it off, you have to put it on and walk around so all of the scientists see you. You can tell they're looking at you when their line of sight is represented by a white dotted line or they will make comments about Joe, the guy you steal the suit from.
In the room you get the shark suit in, there's a door to the break room on the right with about 5 scientists that count towards this achievement. Just open it and get them to look at you or comment and then go up the stairs into the next room where there are 9 scientists scattered around working. Just walk in front of all of them also. Once they all see you, the achievement will unlock.