Superlative form of grubby: most grubby.(adjective)
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Use "grubbiest" in a sentence
"But I always feel underdressed and vaguely unhappy when I wear my grubbiest clothes."
"Once the auditor had departed, Scott donned his grubbiest clothes and a pair of thick work gloves and set about removing the corpse."
"I spend two freakin 'weeks in a developing, central American country, drinking the water and eating food from the grubbiest of tiny little roadside rice and bean huts in the middle of nowhere with no ill effect, but I'm back in my own country for less than 24 hours, and I manage to get food poisoning from something I prepared myself in my own goddamn house."