In Hawaiian, Mahalo means thank you. In slang Egnlish, holler is used playfully as if to say "awesome", "That's what's up!" or "Give me a shout". Maholler is a conjunction of these two words, best used when in Hawaii, meaning "Thank you" or "That was friggin rad!". Only use when much excitement is appropriate.
you- "Hey, I just bought you a bottle of Hawaiian Vodka".