Its not peer pressure I would say. Its also expanding your social circle. "Oh Dan goes on cruises, you know I never thought about it but a cruise does sound fun maybe we can do that instead of visiting the shore next vacation." Stuff like that probably happens on a pretty regular basis I would say.
The usual word of mouth style, just over social media.
I think that in terms of keeping up with the Jonses, people who normally get it bad, get it superbad on facebook. But its like who cares those people usually have their bank accounts pegged to $0 no matter what it can't go any zero'r.