Which episode of How I Met Your Mother does Robin run into that guy at the club?

there's an episode of How I met your mother where everyone's at a club
or bar.. and Robin runs into that guy that I think was an ex
boyfriend, but he thinks she's marrying Ted because Ted announced it
to the entire bar that they're engaged, and at the end of the episode
Future Ted says that it wasn't the end of that guy and Robin,

Does anyone know what episode this is? Or at least which season?

Thanks!!