I don't see the problem with hooking up with a prostitute, at least if it isn't a common occurence. Many guys don't get any women, should they get sexually frustruated while girls go around partying and having sex with every guy they see?
Yeah I know about the stereotype there and i've accepted it. I wouldn't call either of them lonely though, look at Lennard he's meeting lots of women. Also they hang out a lot with eachother. Where I live, the average guy is 100 times more lonely than Sheldon and company. So at the same time it's not really portraited that way. That's why I always find it weird how Penny taunt about "lolol, meet people losers!".
That was one of the examples, but it's more like the whole Penny history that's double standard. First they complain about how they can't meet women and they should do it... But when they do they almost get bashed for it. Whatever they do, they have to take shit because they are "nerds".
Penny didn't seem to like the idea either of what Howard did, and Penny always talks about how many people she has slept with ever since she was young. So Penny is the master of double standard IMO. Maybe you don't think it is double standard, but IT IS as a fact. Howard had to practically beg Bernadotte to come back, by saying he was a jerk and bad person back then.
Whoever she had sex with in the series is irrelevant since she herself has practically referred to the fact that she is sleeping with guys like all the time. At least did. She has probably slept with 100+ herself (Yea I know assumption, but it's portraited quite clearly) : >
Lennard is a bad example as well, he's been sleeping with a lot of women, true. But then the double standard still applies, since Penny is still always taunting about "Hah, like you could meet another women, i'm not worried.". Referring to how she thinks Lennard is unattractive because of his interests. But since Lennard is actually meeting lots of women, she's constantly saying it because of the bias towards the nerd stereotype.