Stale breath
Breath that doesn't smell like much but you can still smell it
"Uncle Judy had stale breath that was unpleasant and unflavored"
Stale-breath
When you're chewing gum for so long that it loses it's taste and starts to make your breath stale.
"I was going to goto the dance with Jimmy but he had such stale-breath that I cringed and I declined his invitation."