Most egregious DCC "offer" I've ever seen - at an ATM at a hotel in Amsterdam (unbranded ATM).

The quoted markup is 16% but based on the rate the charge hit my account at ($121.55) the actual markup was 17%!

Apologies for the glare, but it was a rare sunny day in the Netherlands. The withdrawal was 100 EUR, fee 4,50 EUR (ridiculous enough), quoted rate 1 EUR = 1.36139 USD (rate from Google 1 EUR = 1.15 USD, Visa rate 1E = 1.1632 USD), quoted 'margin' 16.0%, offer amount in USD $142.27.

At least it was easy to opt out ("Continue without conversion"), but still.