Surprised by the responses
My opinion is that a shirt and tie is a must. Its smart, looks professional and as Pilot Pete said it sets a tone, whether you like it or not.
I've seen some really scruffy instructors and to be honest I wouldn't be seen with them sharing a beer, never mind teaching me to fly. One guy I worked with when I was an AFI was so scruffy I quit the job to disassociate myself with him.
Being smart and well presented is an absolute must. I can't imagine turning up to teach in jeans and a tee shirt. How could I expect my students to take me for real???
The day I can't be bothered to don the shirt & tie I will hang my headset up.
Can I ask the guys who think shirts and ties are pretentious what clothing they consider suitable for instructing? Where does the suggestion of it being pretentious come from?