Dropping the name of Meshuggah down, as well as naming specific songs and albums worked for me last time I was at a pub when I was dressed real nice. Was talking to some random dude with Meshuggah shirt, told him I dug the band and he just said, who cares what you look like, you know your shit.
I'm also reminded of a time some girl came to my house with my friend, again me not dressed metal, I had her convinced I was actually a big hip hop and techno fan.
Then she looked through my iTunes list and saw Gojira, Nevermore, Megadeth and Opeth. She cracked the shits at me and thought I was a weirdo