A lesson to everybody ever in the world: Do not invite your ex to your wedding. Simple as that. Robin's arrival at the rushed nuptials and the inclusion of Tony, Stella's ex, were just more problems on top of problems for this wedding that never happened.
Another tragic HIMYM wedding: After some time apart, Ted and Victoria cross paths once again, but this time she's engaged. That doesn't stop Ted and the two drive off into the sunset together, Victoria in her wedding dress. But we all know it wasn't a happy ending. For really, anyone.