Revellers heading to a holiday reunion abused fellow train passengers and exposed themselves, say police.
British Transport Police received complaints about a large group of men and women travelling to Butlins in Skegness, Lincs.
Officers are appealing for witnesses following the trouble on a Nottingham to Skegness train service on Friday.
PC Paul Gleadell said the drunken group "behaved appallingly" for the duration of the trip.
He said the problem started when a group of people, who had been drinking, got on the train at Nottingham.
Pc Gleadell said: "There was a group of about 18 to 20 male adults, who met up with a further group of females all going to a Club 20 reunion at Butlins."