I live in the Seattle area and went to the Rams game the first year Seahawks Stadium opened (2002) and then again the next 4 or 5 years. Wore my Rams jerseys every time. The first year or two were fun. People would heckle you, mostly good naturedly, and then engage in conversation. However, it got progressively worse, to the point that the last time I was there someone wanted to "kick my azz" in the bathroom just because I was wearing the wrong color of shirt. I've been back a couple times since, but no Rams colors.
It's a great area and a good stadium to watch a game, but I'd keep it low key.
