No, its not a lost cause. Our Dori did the same thing when she was 4 mos until about 11mos, although the episodes did decrease as she arrived at 11 mos. We firmly said "No" about hundreds of time, she ignored us, we tried several different things, and finally one day I grabbed her little beard (not hard) but held on to it on each side with both of my hands, brought my face to hers and said "no" and held her there for about 10 seconds, she would back up and just look at me, I would walk off and she would just sit and watch me walk off. Then a period of a few days would go by and we would repeat.....eventually she stopped. Just sharing what worked for us.
She is now 21 mos and she hasn't done this in a looong time.