I think the real point here is the intent behind a question like that. Someone asking a question like "Do I look fat in these jeans" is almost always coming from a place of low self esteem and looking for reassurance. The same goes with a question like "Am I the best lover you have ever had". It isn't that the question shouldn't be asked because you shouldn't be truthful, it's that what you need to be truthful about is the fact that at this point in time the question-asker is feeling insecure/low self esteem/unsure etc. for whatever reason. That is the topic that needs to be discussed openly, not whether you look fat in those jeans.