milinda gunasekera was flying home from a holiday in chile .
he was changing flights at auckland airport for the final leg of his trip .
the 32-year-old downed a bottle of vodka in the airport toilets before flight .
qantas flight was taxiing to the runway when the alleged incident occurred .
afterwards he suffered ` probably the worst hangover of his life ' in the cells .
mr gunasekera will fly back to new zealand to be sentenced in june .