Having retired from international rugby in 2007 after 100 appearances and 40 tries for Wales, as well as captaining the Lions on their 2005 New Zealand tour, Thomas was one of the first high-profile athletes to reveal he was gay when he came out in 2009.
Thomas was invited to the German capital this weekend as a guest coach at the 'Bash About' tournament for 150 predominantly gay rugby players hosted by Berlin Bruisers – Germany's first gay rugby team.
The tournament's concept sees individual players put into mixed up teams with an eight-team competition on Saturday after Friday's coaching clinic.
The event is funded after the club won a grant as part of the initiative "Sportler gegen Stigma" (Sportsmen against Stigma) which promotes the exposure of stigmas and fights against any possible exclusion of sportsmen who are HIV positive.
Featuring players from 20 different gay rugby teams with over 30 nationalities represented, Thomas soon got stuck into the training clinic in north Berlin.
"There are hugely varying standards. Some have played rugby for three months, some for three years, some all their lives, but they are all enthusiastic which means, as a coach, there's nothing you can't do," the 39-year-old told AFP.
"I get asked to do a lot of events, but I will only do them if they have a purpose.
"Rugby gave me a great life and a support mechanism, but what the sport gives you in terms of values and friendships is worth far more.
"These guys are coming on their own to be put into individual teams.
"It can be a lonely existence as a gay guy or woman and rugby is a way of integrating people into a team environment, ultimately giving them friends and a social life.
"When I heard the concept, I just wanted to get involved.
"It's not just about what happens on the pitch, it's about the socializing after and making life-long friendships. That's the whole package of rugby."
Thomas is one of a crop of high-profile athletes to recently come out, including Michael Sams, the first openly gay American footballer to be drafted earlier this year into the NFL, and the Welshman hopes to inspire others.
"I never came out to be an 'ambassador' or 'trailblazer', I came out because I needed to," he said.
"Most of the reaction was positive, but you can't do anything in this life without a bit of negativity, because you can't please everyone all the time.
"I have always focused on the positives, of which there were thousands.
"If you give someone the confidence and self-belief that they won't get a negative reaction, then people are able to be themselves.
"I believe society is changing rapidly and all over the world it is becoming easier to be who you want to be, regardless of how society stereotypically thinks you should behave.
"When I came out, I hoped it would have an empowering effect on other athletes to be able to come out.
"It doesn't matter if they are high-profile, play rugby on a Sunday or just have an interest in sport, I realized it affected a lot of people in a lot of positive ways."
The former Toulouse and Cardiff Blues star finally hung up his boots in 2011 and became a British household name after winning Celebrity Big Brother in 2012, then trying his hand at celebrity ice-skating in ITV's Dancing On Ice.
There are even plans to make a film of his life and he says television appearances presented a welcome opportunity.
"When your life gets so publicized, people can define you in a sentence or paragraph, so it was a way of showing people who I really am and hopefully showing myself in a positive light," he said.
"Stereotypically, so many people thought a guy man acted and behaved in a certain way and most of that was pure ignorance, so it allowed me to get to a lot of more people than I possibly thought I could."
The Welshman is in his natural habitat, joking and encouraging keen rugby players, even if the 6ft 3ins (191cms) former wing or centre occasionally towered over many of the forwards he was coaching.
"It was a little intimidating being coached by him," admitted Australian Ryan Daniel, a second-row from the Stockholm Berserkers club, who moved to Sweden from Brisbane four years ago.
"Especially when he was demonstrating kicking, that's not something you tend to do a lot as a second-row."
Watching Thomas on the sidelines, it suggests he misses playing rugby.
"Not at all. Since I have retired there has not been one day when I have thought 'I wish I was still playing', absolutely never, which shows me that I retired at the right time," he laughed.
"Life is about challenges, I overcame and accepted all of the ones I was given as a rugby player and there weren't many more I could aspire to.
"Now it's all about stepping into the real world and finding challenges and overcoming them, which in the real world is a lot harder."
Based in London, but soon to be moving back to Wales, Thomas now works with schools, coaching rugby and healthy eating to youngsters and working on projects to break down bullying and homophobia in schools.
A Pantomime season in Cardiff beckons this Christmas after his autobiography comes out in September which promises to tell the real story.
His first attempt 'Alfie! – published six months before he came out – did not mention he is gay.
But for now, his main challenge involves deciding what to sing in the after-party Karaoke competition in the heart of Berlin's throbbing nightlife.
"Apparently everyone has to sing, which I don't mind, but I have heard people have been rehearsing, so I am wary. Karaoke has to be rubbish for it to be good," he insisted.
"Everyone thinks that as a Welshman you can sing. I don't know where that myth came from, but I will smash that – big time."
"I like a bit of 'Sweet Caroline', which works well in Welsh pubs, but I might give them a surprise and go for something from Witney Houston like "I Wanna Dance With Somebody".
"If it gets everyone on the dance floor – target achieved."