1. An unmade bed
In my single days, I can't tell you how many people's beds were unmade before they tried to get me into them. Too many, I'll say that.
I'm unsure what kind of person expects somebody to hop into a bed that remains messy from the night before.
It might not be dirty, but it looks dirty. It might not smell, but it looks smelly. An unmade bed is the number one most obvious turnoff that everybody notices when going into someone's room for the first time.
2. Posters of naked people
Want to tell somebody that you're about to have sex with that you're too juvenile for sex? Keep those posters from Sports Illustrated up on your bedroom walls.
If you still hang up A3 images of busty ladies or have a naked firefighter calendar up on your door, you're sending a clear message: "I still think of sex as a dream, not a reality".
Take them down and put up a cheap Kmart canvas instead if you must.
3. Saying you hate your body
Adding in a verbal disclaimer about how insecure you are about your body before you undress for the first time is problematic. You are essentially fishing for a compliment (and no matter what reply you get, it probably won't be genuine).
Most people aren't 100 per cent comfortable in their naked bodies, but saying that you hate yours will not make you seem more attractive.
Need some reassurance that somebody finds your body hot? They're in your bedroom taking your clothes off. We should all accept that as sufficient.
4. Saying "I don't do ..."
It's okay to be uncomfortable doing some things in bed. We all are. Nobody likes everything.
However, when you start telling someone what you don't do (e.g. "I don't go down on girls"), it's presumptive and affronting. Especially if there have been no movements towards that particular act and you're literally just restricting your impending coitus.
Don't confuse this with recommending you should do things you don't want to do on a first date – that goes explicitly against our modern ideals of consenting sex – but it's a turn-off to give a potential partner a list of no-go zones before they've even kissed you properly.
5. Telling someone they're doing something wrong
I've been with a few people who have tried to micro-manage sex from the get-go. The kind of people who think they know what they like, and how they like it, and have no tolerance for anything else.
They'll tell you, in the moment, that you're doing something wrong – "you're not kissing enough", "you're not using your hands enough", "you're not paying enough attention to this/that"... and so on. It's a nerve-wracking and exhausting experience.
It's selfish and a huge turn-off if you're the one doing it. I like to hope we can all leave the constructive criticism until a relationship is more serious, and you can more freely express your wants and needs in a safer space.