According to Official Guinness Records,
The most whoopee cushions sat on in 30 seconds is 54 and was achieved by Matt Bray (USA) in Naperville, Illinois, USA, on 18 April 2015. Matt previously held this record with 37 whoopee cushions before losing it in 2013.
For a complete list of 2015 records, please visit 2015 Guinness Records in United States.