Hi!
As long as you don't want to sell anything, you can go to Farnborough and Le Bourget on any day wearing whatever you like. Been there at least ten times since 1982 (more often to Paris than to F'boro) as engineering student, pilot and co-owner of an air taxi outfit. I never have worn a suit in all my life, never owned one. They want to sell you aeoplanes, not fashion!