ゲロ = vomit
シヴ = civilization
It could mean a suit that is reminiscent of bum/dirtbag, non-conformist, dadaist, or punk (or any combination of these, for that matter) culture. This could possibly be related to what you read that involved bikes and cars in the sense of punk roughly equivocating biker or dragracer, if those are the types of bikes and cars we ...
ゲロシブ splits into the part of ゲロ and シブ.
シブい comes from 渋み. It describes bitterness or a bit of sourness. The aesthetic nuance describes maturity, so it's actually fashionable not in a so young and fresh way. Probably it means “dandy” in this context.
ゲロ literally means “a vomit”, but it is simply used as an intensifier like “damn” cool or “badass”.
Thus the ...