My husband and I had an Adventure Time themed wedding a month ago and we turned a whole slew of people into fans that way - our cake baker, some of the venue staff, a whole bunch of our friends and family. Unlike MLP and other shows where I feel like I have to explain things for people to get started, AT is generally great enough that I just tell people to watch any episode and then just blow their minds explaining some of what's going on in the show at large that they might not have picked up on. Love it.
Cake (and we even got CN's permission for it! suck it disney!): https://www.flickr.com/photos/argon/13347167874/
His and hers flowers with Finn and BMO: https://scontent-a-sjc.xx.fbcdn.net/hphotos-ash3/t1.0-9/p480...
And one of the centerpieces ;) https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-prn1/t1.0-...