According to Official Guinness Records,
The record for the most people shaving with an electric shaver (multiple venue) is 1,421 participants and was organized by Panasonic Corporation & Gamba Osaka Co.,Ltd. (Japan) at the Expo ’70 Commemorative Stadium in Osaka, Japan on 3 November 2011.
This event was part of the 'Most people shaving with an electric shaver (multiple venues)' attempt which was achieved by 1,981 participants. The challenge was a promotional event held before a football game.
For a complete list of 2011 records, please visit 2011 Guinness Records in Japan.