I was led into a viper ambush by a molerat, outsmarted by vermin.
Vermin? HOW DARE YOU SIR!
As for the most memorable moment? Hmm.. I don't know if I can single one specific moment out, but I'll list a few:
Finally talking to Ulysses.
Leaving the Sierra Madre after dealing with Elijah (that's when the whole theme of the DLC hit me).
Finding the Survivalist's skeleton after reading all of his terminal entries.
Talking to House about the future of Vegas.
Eh, I've listed too many... but they were all memorable.