If I wanted to increase the grungy look of my bike (a few posts above) I'd mismatch the following:
Cranks
Pedals
Wheels (already done) - if spokes also mismatch / shiny / black - even better
Mudguards (already done)
Handlebar grips
Change bell for dog's squeaky toy - more outrageous the better imo - have just put one on my Ebike.
Rubbish but subtle paint job - but not matt black or pink - just screams overpainting to me. (check how experienced model makers 'weather' their models)
Kids bike reflectors on spokes
Battered cardboard box on top of an old but serviceable rack - tied down with string.
Change handlebar (with one of same spec) for one that's visibly cosmetically challenged.