Looks like another one for the bugged list.
This should unlock at the end of Bobs questline , after you
you return to bob and disagree and give him a hard time. There was some speculation on the steam guide you had to do it in two runs agreeing and disagreeing with Bob so I did twice choosing different dialogue each time. and no achievement.
UPDATE: I've tried twice for this since the new patch that fixed the other achievements and both times it's glitched and bob stays on the 1st floor. This happened to me before but I was able to quit and go back and find him in the tycoons mansion to speak to him but now he just vanishes.
I'll play around with it some more time permitting and post if I find a work around.
UPDATE 2 This now obtainable. You need to do Bobs questline twice , even if you have already done it before the patch it won't unlock automatically. For this you need to get to the end of bob's quest and fully agree with him and then do the opposite in a second playthrough.