Would you say it is rude to ask this to a teacher?

My friend was singing 'Moulin Rouge' and asked me the meaning so I asked the teacher that she wanted to know what 'Voulez vouz coucher avec moi?' meant and she was getting really steamed saying how I'm so rude because I asked the teacher such a thing. I don't care too much for her opinion but I just wanted to know if it is rude to ask that to a teacher cos sometimes I do things that people say are stupid or rude etc