I'm surprised no one has suggested this yet. If it's too hot, I politely ask the cabin crew to "check whether the temperature is set right as it seems to be very warm". 90% of the time they fix it. The other 10% I've been told rightly or wrongly "there seems to be something wrong with the temperature regulation, nothing we can do". On one of those occasions (F in an A380) they suggested I go sit in the area in front of F by the stairwell to cool down as "it's lovely and cool there", so on that occasion at least I don't think it was made up.

I guess I could also have threatened to remove some clothes. That would have frightened them into turning the temperature down.