Causes of uneven brake pad wear?

[map]

Just going into diagnostic mode as my lad changed his chain and sprockets last night.
I noticed one side of the rear brake pad was worn more like a wedge shape. Very uneven.

So just wanted a sanity chaeck what the cause might be.
I have my own thoughts but thought it worth getting other suggestions (even if they just validate mine if nothing else).

Bike is Varadero XL125V with single pot rear brake.

I will get around to persuade him to remove calliper and strip it down.

<gripe mode on>
That's when he can get his act together and get the replacement break fluid and can tear himself away from his girlfriend.
This is the lad who left the socket set out in the rain
I spent an hour cleaning and drying each part and the box because 'he had to go out'.
<gripe mode off>

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Gibbs, what did Duckie look like when he was younger?

[Islander]

That tends to suggest that the pad isn't moving freely in the caliper. It'll need the pads out to check that. Clean any crap in there out. The other less likely cause is that the caliper isn't sliding freely on its pins (assuming it's a floating caliper) - if that's the case then it's strip, clean, lubricate.

ETA

Remember what your own priorities were when you were his age...

[Vincent]

Any pics of the pad......and caliper?
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