VariablePitchp is spot on! Honestly it makes me cringe some of the things I read on pprune. You wear smart causal when you meet your friends, if I’m assessing you and you show up without a tie, I’ll send you home. I know that the school will put in their report to the airline , what you were wearing. This is an adult job in mature industry, it goes without saying that you should act and look as such. Remember that British Airways wants you to be an ambassador for their brand, and they want to see someone with high personal standards.