On departing Manchester Intl once, I was asked if I could make an immediate departure. Agreed yes (otherwise a 15-minute hold for other important traffic) and lined up still completing the checks. Tower cleared me for immediate take-off with an early left turn and cleared a company aircraft onto the runway behind. As I got to about 50kts, noticed rather a lot more wind in the cockpit than usual... Ooops, shut the door! Aborted the take-off down an RET, told the tower I had a small tech-snag and would be ready in 1 minute. Company aircraft rotated right next to me and said "Check the door before the next departure!!" as he flew by. Ho hum.
Forgotten the chocks once as well....!