"barking mad" meaning in English

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "barking#Etymology_1",
        "3": "mad"
      },
      "expansion": "barking + mad",
      "name": "com"
    }
  ],
  "etymology_text": "barking + mad",
  "head_templates": [
    {
      "args": {
        "1": "-",
        "nolinkhead": "1"
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      "expansion": "barking mad (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "British English",
          "parents": [],
          "source": "w"
        },
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          "source": "w"
        },
        {
          "kind": "other",
          "name": "New Zealand English",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Completely insane."
      ],
      "id": "en-barking_mad-en-adj-~ScVsc3x",
      "links": [
        [
          "insane",
          "insane"
        ]
      ],
      "raw_glosses": [
        "(British, New Zealand, informal) Completely insane."
      ],
      "synonyms": [
        {
          "word": "three stops short of Dagenham"
        },
        {
          "word": "insane"
        }
      ],
      "tags": [
        "British",
        "New-Zealand",
        "informal",
        "not-comparable"
      ]
    }
  ],
  "word": "barking mad"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "en",
        "2": "barking#Etymology_1",
        "3": "mad"
      },
      "expansion": "barking + mad",
      "name": "com"
    }
  ],
  "etymology_text": "barking + mad",
  "head_templates": [
    {
      "args": {
        "1": "-",
        "nolinkhead": "1"
      },
      "expansion": "barking mad (not comparable)",
      "name": "en-adj"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        "British English",
        "English adjectives",
        "English compound adjectives",
        "English compound terms",
        "English entries with incorrect language header",
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      ],
      "glosses": [
        "Completely insane."
      ],
      "links": [
        [
          "insane",
          "insane"
        ]
      ],
      "raw_glosses": [
        "(British, New Zealand, informal) Completely insane."
      ],
      "synonyms": [
        {
          "word": "three stops short of Dagenham"
        },
        {
          "word": "insane"
        }
      ],
      "tags": [
        "British",
        "New-Zealand",
        "informal",
        "not-comparable"
      ]
    }
  ],
  "word": "barking mad"
}