I went to London Welsh a few years ago for a 6N England game with 2 english friends, 1 of their Irish girlfriends and my Scottish girlfriend at the time... in a marquee of about 2000 people, they were the only 4 non-Welsh there!! There was this Welsh guy who was giving them abuse constantly, until about 35 minutes in when about 100 Welsh guys started shouting at him for being a "football supporter" and calling him a tw@t... they made him buy all 5 of us drinks for the entire match! We eventually bought him a drink at the end of the game... he seemed happy enough even though Wales lost.
I would lend you a Welsh jersey.. but doubt it would fit.
No doubt at all but thanks H for the very considerate offer