Everyone has done something they regret during sex. Awkward situations and hurt feelings can be avoided by simply not doing certain simple things.
Not informing someone of an infection
Even if your infection does not affect your genitals, no one wants to find any infection in the dark.
Oral sex gas
Passing gas while your partner is performing oral sex on you is unacceptable. Imagine what they are getting a face full of, and how likely he or she would be to perform oral sex on you again.
Calling your partner by the wrong name
If this happens, feel free to follow up with, "I was just making sure you were paying attention."
Bringing crabs to the party
Parasitic genital lice are not sexy. They may not be harmful, but are irritating and will give you a bad reputation - especially if you are supposed to be in a monogamous relationship.
Falling asleep during sex
There is no better way to tell your partner that they are boring in bed. If you are falling asleep or very tired, let your partner know ahead of time so they are not shocked and/or disappointed.
Knocking your partner off of the bed
Some positions require a lot of balance. Make sure that the motions you are making does not send your partner tumbling to the floor.
Demeaning dirty talk
Dirty talk is a common activity in sex. Know the difference between saying, "I want to get you off." and "I'm going to fuck you, you dirty whore." Discuss the use of derogatory and demeaning words before employing them.
Asking if your partner loves you
You are likely to get the answer you want, but remember that he or she is not really thinking clearly about their response. Putting someone on the spot is a great way to kill the mood.
Asking if it's in yet
This is the equivalent of asking a woman if she thinks she's gotten fat enough. This emasculating line can be avoided by putting your hand down there and checking. If it's not, guide it in. If it is, hold your comments in and find a more appropriate partner.
Telling your partner you are the opposite gender, or letting them find out on his or her own
Only an issue with a first time sex partner, be clear about your gender well before you get someone in the bedroom. This is not a time where the truth should speak for itself.
Faux pas happen in sex. Try to avoid faux pas to ensure that both you and your partner enjoy themselves the most, and that you do not get a reputation as a bad lover.