Here's what rhymes with maddeningly.

Consider these alternatives

frustratingly / rustratingly annoyingly / cloyingly excruciatingly / unhesitatingly maddening / happening exasperatingly / unhesitatingly irritatingly / unhesitatingly imprecise / price agonizingly / antagonizingly hilariously / variously comically / chronically mystifying / dying inscrutable / suitable astoundingly / resoundingly tantalizingly / surprisingly