Demonstrate how to go mad with vehicle? (5-5)

I believe the answer is:

potty-train

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'demonstrate how to' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'mad with vehicle?' is the wordplay.
'mad' becomes 'potty' (informal term).
'with' means one lot of letters go next to another.
'vehicle?' becomes 'train'.
'potty'+'train'='POTTY-TRAIN'

'go' is the link.

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I've seen this clue in The Times.

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