Would you be upset if your partner lied to you about watching porn?

I agree with this. I don't think it's okay to lie, really, but when you're in a relationship, and let's say, things are going well, you're really into the other person, and then they say something like, "I hate porn, and it's a total deal breaker for me," you'd probably think, "well, I can't tell her about looking at porn, now. She'll leave, and I love her!" So that's where the lie starts. But perhaps he didn't want her to have so much control over his life that he'd stop watching porn altogether, because that's a personal decision for him to make.

But I'd be more upset about the lie than watching porn, because I watch porn, 99% of men and a large portion of women too watch porn, and I'd love to watch it with him! The lie is the issue, as is the expectation that he isn't allowed to look at it because of her personal preferences and views on pornography. It could very well be a sign of incompatibility. For me, a deal breaker would be the expectation that I not look at porn, because of how my partner feels about it. This is why it's important to be open about yourself with your partner in the beginning and disclose any kind of sexual taste, preference, kink, need, expectation, etc. before these little lies start and then get out of control. Some people don't want their partners viewing porn. Some don't care. But everyone wants their partner to be honest and truthful.

absolutely agree with you on that

I wouldnt be mad but I would think it was ridiculous to lie about, nothing wrong with watching porn. But if your sister made it seem like it was a bad disgusting thing I could see why he lied

Is too!

I absolutely agree. Sadly the intolerant come in many guises. So, many of us simply have to do what we have to do, to survive.

Nope, no snooping.
Porn became the topic of conversation and he contradicted what he said in the past.

Also, the porn bit doesn't exactly upset her. It was mostly just the lying about something so small.

In all likelihood the young man was embarrassed about it. There are innumerable reasons. A rather plausible one would be that by admitting to looking at porn he was also outing himself that he masturbates. As odd as it may sound many men are simply very uncomfortable admitting to that particular pleasure. I see absolutely no reason for your sister to be upset about something so very trivial. Unless her being upset is for her a convenient reason to dump the guy.

He was probably embarrassed to tell her he was watching it or maybe he did not want her to get mad...depends on why he lied about it.

I don't know why he would have to lie. I guess if he did, I would want to know why he felt that way.

I would be upset about the lie. Not about the porn! Lying is baddd