Let me shed some light into the matter, Mahira Khan and Ranbir Kapoor are not dating. They're merely friends and met at an event in Dubai. Mahira has a home in America and celebrities outside their profession can hang out. Mahira specifically cleared doubts of her 'dating' Ranbir Kapoor a while back since he confessed he finds her 'pretty' and Bollywood made something out of it.
Mahira Khan was always a smoker, however we need to question what led her to smoking, she's had a broken Marriage, a single Mum and is a workaholic. The dynamics in her life or the circumstances is what may have pushed her to such barriers. Stressed and over-worked. We don't know and we shouldn't judge.
The mark on her back is a birth mark, not a tattoo. Something she was considering removing, however in previous dramas where she has backless on - it has been covered with make up. There goes the other judging point regarding the 'tattoo'.
Further to that she is non-religious, an actress and what she wore was outside of Pakistan.
Lastly, the reaction of the typical Pakistani community is non-surprising and is understandable. You guys have PEMRA for everything, a cartoon called 'Winx Club' was banned in Pakistan due to 'inappropriate clothing'.
Pakistan has cultural norms and values, in all honesty even in the West a Woman smoking is frowned upon so why is there an expectation of an advancement in mentality when this ideology till date is still a struggle to adjust with in the West?
I hope I've given a non-biased fair point to both sides. In the end, each to their own.