I honestly didn't know what you meant by BM. It was like a cryptic crossword clue. I've gone through BMW, the British monarchy, Birmingham Midshires, Barry Manilow, Bertie Mee, blame me, bugger me, Balamory, be me, be someone else, be a bee, be a bee being me, be Bertie Mee being a bee being me...
Three hours later, I guessed it may be bowel movement. It is, isn't it? If so, you don't need to take your clothes off.
I have read of many people who find it comforting to remove all clothing for purposes of a BM. It may be something going back to childhood, or even a worry about the cleanliness of one's clothing. Who knows. But, I do know this is of a normal concern.
On a western style toilet I never do that but while in India if it was an Indian style toilet I did that because it's difficult to shit with your pants down and splash water to clean your ass without wetting them.
Three hours later, I guessed it may be bowel movement. It is, isn't it? If so, you don't need to take your clothes off.
Uncryptically, the answer is no.