If you are going to post on Smackjeeves, be extremely careful with your cover image. The owner of that site is rather prudeish and nitpicky. You can be singled out for something so plain as having a black border on your cover. There are no clearly outlined rules for how these covers are allowed to be set up last time I checked, and it seems the rules just vary as the site owner feels.
If your comic becomes very popular you can also get sacked big time for mature content. Smackjeeves had an infamous yaoi purge a few years back, and it's most likely one of the major reasons it's so dead now.
Like with tapas, you have to keep all sexually displayed genitalia censored. Censorship requirements may actually be stricter on smackjeeves, I wouldn't know since, once again, I have never seen a clear definition nor received one in contact with the site owner, and it seems the rules vary randomly depending on the owner's mood. I am open to having my mind changed if anyone else can provide evidence that this tendency has improved on Smackjeeves.
From my understanding, having posted a yaoi comic on tapas for a couple years now and having had to communicate with staff about censorship on said comic, the censorship requirements on Tapas work as I have previously outlined:
Expect the same guidelines for smackjeeves but beware that it might be/become stricter.
The "I know it when I see it" attitude about erotic content needs to stop and be replaced by extremely clear and abstract, logically detailed guidelines, or it will continue to be subject to potential abuse. Then again, if I may be free to say whatever I want, then I think taboos on sex need to die in general. The way I see it, sexual activity is no different from sports or eating cake. Some people need it to stay healthy, some people just get the occasional craving for it, some people would rather not. Regardless, sports and cake should be free to be enjoyed anywhere as long as everyone involved wants it, and people who don't want to be involved should neither be pressured into it, nor should they hold any right to tell people they can't have cake "because I don't want cake!!!!"
Unless you're whipping out your cake in the middle of class, a funeral or at a hospital, etc. Other situations where it would be disruptive.
But that's just me ¯_(ツ)_/¯