Whether you are President of the United States or just an average Joe, there are at least 8 instances when it is absolutely wrong to tell a woman she is hot. No matter how hot she is.
It is always inappropriate to tell a woman she is hot if:
1. You work together.
Whether you are coworkers at the same level or the hot girl is your boss or your subordinate, it is never appropriate to tell a coworker that you think she is hot. Not only would that be entirely inappropriate and might make the coworker feel uncomfortable but it could lead to a compulsory visit with the HR Department for a lengthy lecture on sexual harassment in the workplace. No one has time for that.
2. You are a priest.
Hahaha. Just threw that in for a laugh. But it's still true.
3. The woman is trying to engage you on an intellectual level.
Nothing says scumbag more loudly that a man responding to a woman's intellectual argument with a line like this: "Damn, you are so hot when you discuss capital punishment." Even if her position on capital punishment agrees with your position on capital punishment, it will not end well for you if she thinks that all you can focus on are her breasts, not the point she is making.
4. She is your mother-in-law.
Your mother-in-law may be a really hot woman and she may have given birth to a really hot daughter who you managed to marry but there is something fundamentally wrong about a thought that includes both a sexy body and a mother-in-law. It's just beyond icky. The prohibition also applies to telling your daughter that she looks hot.
5. She is your patient and you are a gynocologist.
In fact, this also holds true for any doctor or nurse or medical professional. It also applies to therapists. Whether you are actually bare naked on an examining table or baring the naked truth on the therapist's couch, you'd like to think your hotness wasn't at the forefront of the doctor, nurse or therapist's mind.
6. You have never met the woman.
Some men will disagree about this one especially if the woman is dressed in tight and revealing clothing and is pole dancing in a bar but I say it is inappropriate to tell a woman she is hot if you've never met her or have just met her. If she really is hot, probably everyone in view is thinking the same thing but you will look like the guy who is lacking a filter by just blurting out the obvious.
7. You are a cop and you've just pulled over a woman for speeding.
You might be able to get away with saying, "You must have been speeding with the windows open because it is 100 degrees out and you are so hot." But without all of those caveats it would be best not to mention the woman's hotness. Just tell her to slow it down and don't give her a ticket if you don't want to. It's a fact that hot women get fewer speeding tickets.
8. You and the woman are both at a sexual harassment seminar.
"You are so hot" is probably not your best opening line if you meet a woman at a sexual harassment seminar. Stick with topics such as the weather, the GDP, or climate change.
In sum, it is always appropriate to tell your wife/girlfriend/significant other that she is hot but best to avoid saying it to anyone else. The hot ones know they're hot so you're not telling them anything they don't already know anyway. But you can think it all you want!