When, if ever, is it acceptable to wear a HRM during sexual activity?

Some websites allow you to estimate calories burned during different physical activities. I am fairly familiar with many of these websites, as well as similar iPhone apps, and I regularly see "sexual activity" as an activity option. Now this didn't really strike me as odd until I purchased my Polar FT7 heart rate monitor.

You cannot truly know how many calories you burned during a particular activity unless you wear a heart rate monitor programmed to your settings. These estimation websites are based off of other people's data and mathematical formulas. I understand how a website could ask 10 different people to run a 9 minute mile while wearing a chest strap and HRM, and then use this data to generate a formula, but has anyone been asked to wear a chest strap and HRM during sexual activity?

This brings me to my true question: Is it socially acceptable to wear a heart rate monitor while having sex?  I think I would genuinely like to know how many calories I burn in let's say, 20 minutes. There was a point in my life when sexual activity was my main (okay, only) form of exercise, and it would have been nice to know if I was making any significant impact in burning the fat off my thighs.

I first thought that you could probably get away with wearing a HRM while having sex with someone you probably won't be having sex with again, (what do you care if they think you're weird? it's not like you're planning on eating breakfast with them) but then I realized you want to use this with the person you sleep with most frequently so that you can consider the calories burned as standard for the duration of the relationship. I'm not sure what to tell you if you're not practicing monogamy.