Start a band that includes BOTH a ukulele and an accordion. Sing about birds and stuff in a soft tone as if you're high as a kite, because you probably are. Bonus points if you're trying to rip off the White Stripes.
Ironic clothing is also a must. I once had to tape a hipster band for some local TV show. Drummer had a grey hoodie with the word "GREY" emboldened on it. Wearing a loose fitting touque in the summer also helps.