I like logo t-shirts without the phrase, he's why. The logo is (or can be) an identifiable brand, but the pithy catch phrase is not likely going to be part of your brand. And certainly do not make reference to any forum specific behaviors, we enjoy the community here, but forums are not generally thought of as cool and can be daunting for new members. Anything that denotes attitude is not going to attract new members.
As for the type of shirt, you need it to be something that can be worn on the golf course, not our doing chores. This is a community of people that buy golf shirts, so make it a golf shirt (wicking material, polo). The challenge is getting folks to buy them for $80 because it's not cheap to get custom, good polo's.