The groom-to-be and five of his friends could face fines of up to 25,000 euros ($27,000), according to the police.
The British nationals were "under the influence of alcohol" while flying from London to Bratislava for a bachelor party late Saturday, authorities said. They allegedly refused to stay in their seats, clashed with the cabin crew and started behaving aggressively after they were refused alcohol. One of the men reportedly took his clothes off.
Eventually, the crew determined they "misbehaved so badly" that the pilot decided to divert the plane to Berlin's Schoenefeld airport.
Berlin police detained six of the alleged offenders, all aged between 25 and 28 and hailing from Southampton in southern England. Another six people from the same group were allowed to stay on board.
"We will not tolerate unruly or disruptive behavior at any time and the safety and comfort of our customers, crew and aircraft is our number one priority," Ryanair said in a statement quoted by Southampton's Daily Echo.
"This is now a matter for local police," the company added.
After the stop in Berlin, the remaining 164 passengers were able to continue their flight to Bratislava.
The British nationals were released after several hours. In addition to high fines, they could also be targeted with civil claims from the low-cost airline.
dj/jlw (AFP, AP, dpa)