I was re-watching Sandcastles in the Sand (for the 1000th time xD) and I thought that it would be fun to write out the end scene as like a kind of 粉丝 fiction. This story is told in the third person but it's from Robin's POV.
When Ted attends his mother's wedding, he is extremely disturbed 由 her overly affectionate relationship with her fianc, which forces him to think about his own life and make an impulsive decision.
When Marshall gets mugged, Lily decides she wants to get a gun for protection, so Marshall comes up with a convoluted story about the mugging to deter Lily from following through.