Hm, how about - do NOT drink hot drinks from this type of plastic cups? There is a reason why they deform - the type of plastic used. They are not designed for hot drinks. They deform and release chemicals into your coffee. If it's only sometimes, ok. You will not live long enough in order to be harmed. But it's not a good idea to have this coffee every day.
There are plastic cups for hot drinks and they are harder and whiter. At least they are designed with the idea that the contents will be hot so you can hope that the type of plastic used was ok.