He is the groomsman of my wedding.

结婚的时候，他是伴郎。

Would you like to be my groomsman?

你愿意做我的伴郎吗？

You are my groomsman.

你是我的伴郎啊。

She shacked up with some groomsman or something?

她和某伴郎有一腿吗?。

My friend Alan invited me as his groomsman at the wedding.

我的朋友Alan邀请我在他的婚礼上担任伴郎。