My favourite was at the Stoop a few years ago, when Kyle Eastmond got sent off & Wasps battered Quins playing with 14 men for most of the match.
I had been lent my friends Quins season tickets for that game so my wife & I were the only Wasps fans in a sea of quartered shirts. The sheer joy of standing up cheering every time we scored, surrounded by an increasingly unhappy crowd, was just wonderful!