1. most crumbly; breaking apart most easily into small pieces
Usage: superlative form of crumby
2. worst in quality; most inferior or unpleasant
Usage: informal; superlative form of crummy

Examples

• This is the crumbiest cookie I’ve ever made.
• The old cake was the crumbiest part of the dessert table.
• That was the crumbiest movie we saw all summer.
• He gave the crumbiest excuse for being late.
• The crumbiest cheese fell apart when I tried to slice it.
• She had the crumbiest luck with her car breaking down again.