For starters, it is not uncommon for some not to say thanks when someone does something positive so no need to be surprised here. The problem is when the employee continues to take it for granted what others do for him or her feeling like an entitlement. If the manager or co-workers remain helpful to this individual and don’t get any recognition for it then it is time to think about whether this is simply manipulation and/or on the other side enabling so it is your choice, right?