When is it socially acceptable for a man to wear a kilt?
Assuming the answer asks in the context of modern Western culture: On any formal occasion.
It is acceptable for a man to wear a kilt on a formal occasion, such as a wedding, christening, funeral, part of a military uniform, etc. provided he has some credible reason for doing so, such as Irish (it is an Irish invention*) or Scottish heritage, membership or service in selected military units [1].
Absent these reasons, wearing a kilt will be seen as a fashion statement at best and would provoke either discomfort or amusement in others at worst.
For myself (no service in the armed forces):
Would I wear a kilt into the office on a random Tuesday? No, but a kilt is not provided for under my company's dress code (I work for a multi-national).
Would I wear a kilt for going to the shops? Yes.
Would I wear a kilt to my wedding? Yes, and I will some day.
* the kilt 'proper' that is, the x-yards of fabric one. The 'skirt' version was invented in the 19th Century [2].
https://en.wikipedia.org/wiki/Kilt
https://scottishkiltshop.com/blog/is-it-offensive-for-non-scots-to-wear-kilts/
https://scottishkiltshop.com/campbell-tartan-kilt.html
Assuming the answer asks in the context of modern Western culture: On any formal occasion.
It is acceptable for a man to wear a kilt on a formal occasion, such as a wedding, christening, funeral, part of a military uniform, etc. provided he has some credible reason for doing so, such as Irish (it is an Irish invention*) or Scottish heritage, membership or service in selected military units [1].
Absent these reasons, wearing a kilt will be seen as a fashion statement at best and would provoke either discomfort or amusement in others at worst.
For myself (no service in the armed forces):
Would I wear a kilt into the office on a random Tuesday? No, but a kilt is not provided for under my company's dress code (I work for a multi-national).
Would I wear a kilt for going to the shops? Yes.
Would I wear a kilt to my wedding? Yes, and I will some day.
* the kilt 'proper' that is, the x-yards of fabric one. The 'skirt' version was invented in the 19th Century [2].
https://en.wikipedia.org/wiki/Kilt
https://scottishkiltshop.com/blog/is-it-offensive-for-non-scots-to-wear-kilts/
https://scottishkiltshop.com/campbell-tartan-kilt.html