fucking bullshit solution

Janky_Bullshit.js

var arr1 = [
    [21, "Bowling Ball"],
    [2, "Dirty Sock"],
    [1, "Hair Pin"],
    [5, "Microphone"]
];

var arr2 = [
    [2, "Hair Pin"],
    [3, "Half-Eaten Apple"],
    [67, "Bowling Ball"],
    [7, "Toothpaste"]
];

var merged = arr1.concat(arr2);

var JSON_merged = {};

for(var i in merged){
    JSON_merged[merged[i][1]] = merged[i][0];
}

var merged = [];

for(var prop in JSON_merged){
    if(JSON_merged.hasOwnProperty(prop)){
        merged.push([JSON_merged[prop], prop]);
    }
}

console.log(merged);

/* output:
     [ [ 67, 'Bowling Ball' ],
     [ 2, 'Dirty Sock' ],
     [ 2, 'Hair Pin' ],
     [ 5, 'Microphone' ],
     [ 3, 'Half-Eaten Apple' ],
     [ 7, 'Toothpaste' ] ]
 */