It's hard to choose, but I'd say King Dedede, Whispy Woods, Kracko, and Meta Knight 'cause they're among the most persistent bosses in Kirby history. Also, Dyna Blade, Marx, 02, and Nightmare.
Joe: Spill your guts, tubby!
Dedede: Eh, tubby?!
Escargoon: Hey wise guy, this is the king you're talking about! You can't insult him because he's fat! Or because he's a big ignoramous! Or because he's a tightwad- *gets smashed with Dedede's mallet*
~Here Comes the Son
Escargoon: Kitcheeennn!!!! Where's the chow, ya chowderheads?! His highness is hungry up here!
Waddle Doo: But we just served the King a 10-course meal!
Dedede: All of them appetizers was un-appetizin'! Bring me 10 different courses and make it snappy!
Waddle Doo: Right! *he and the Waddle Dees finish the 10 courses and bring the food to Dedede* Hup, two, three, four, we bring the food and he wants more! Five, six, seven, eight, the King had better watch his weight!
~Hour of the WolfWrath