Instructor pilot flying right seat in a B-55 Baron reported the pilot flying mistakenly retracted the landing gear instead of the flaps on the takeoff roll; resulting in damage to the propellers and landing gear doors.

Narrative

I am a ME CFI with over 25;000 hours total time and over 3;000 instructing.A friend was going to loan another pilot his Baron so that I could get her ready for her ME rating. The friend was a commercially rated ME pilot who had over 600 hours in the Baron.He flew to ZZZ1 Airport and I flew the Baron from the right side with him to ZZZ airport to make three takeoff and landings to become current. The first landing was to a full stop.I took off again and came around the pattern. I suggested a touch and go since it was a 4;200 foot runway. I was in the right seat and I advised him that I would handle the power and asked him to retract the flaps on the takeoff roll.Unfortunately and unknown to me; he brought the gear up instead which caused the gear to collapse as I was beginning to rotate the airplane. It settled back onto the runway and skidded off to the side on the Baron's belly.Neither of us were injured but the propellers hit the ground and brought the engines to a quick stop. Props and gear doors were damaged.The owner/pilot said that he didn't know why he grabbed the wrong control. On the Baron; the flap and gear controls are reversed from most other aircraft with the flap control on the left side and the gear control on the right side. Perhaps I should have stressed this on the briefing but he had three times as much experience in the Baron as me.I will stop doing touch and go landings on complex airplanes and probably quit instructing ME altogether