I'm disappointed only 3 people have voted in my poll
The reason is that your poll choices are incomplete.
There is no single answer. It depends on the occasion.
In my personal opinion :
a) If the WAG (Wife and Girlfriend) likes the lingerie then she should be the one to buy it (assuming she is earning an income otherwise a few persuasive words to her HOB will settle the matter quickly
b) If the HOB (Husband or Boyfriend) likes the lingerie then he should ask his WAG opinion first whether she likes it before he buys and pays for it. This shows respect for his partner's feeling and consideration. There is a possibility that what he finds appealing may be considered non appealing or "non acceptable" (e.g. because it is too flouting) according to his WAG.
Some people are more conservative than others based on their personal upbringing/background and find certain lingerie to be too revealing to be comfortable emotionally for them to wear. People have different taste. Beauty is in the eye of the beholder.
Of course, he can buy the lingerie first and ask later but will then risk wasting his money unecessarily. It would be better to consult and the couple will likely end up with a choice that will tick both of their boxes and gives more guarantee to provide a satisfying result. If it becomes a choice desired by both and they earn a salary then the cost can be split if both insist on paying. The easiest would be 50/50. An alternative choice would be salary based e.g. the person earning double the income of the other will pay 2/3 of the cost.
There is no single answer and hence there is no vote