A lot of Thais find this offensive and disrespectful.
I was with a mate in a Bangkok dept store. He wanted to buy some t-shirts but try before you buy. Now, my mate ex-biker type with some good tats began to take his shirt off near the t-shirt stand. What he missed out on was most of the girls serving in this section were all waiting for him to go in the change rooms to try the gear on. The store girls were intrigued with his tats on the arms and wanted to see more. The need was to educate my friend on the customs very quickly in order to have maximum impact.
The moral of the story is to respect the customs of the land you are visiting to enjoy maximum benefit.
The next Dept store we went too, being more respectful he ended up on taking one of the store girls out to compare Tats.