Probably top of the list of "should not" is to use inappropriate examples or images to liven up proceedings. Recently I attended the 6th Joint Sheffield Conference on Chemoinformatics (more here at NM) and saw red when a speaker talking about ways to rank docking programs decided to use contestants in Miss World as an illustrative example, complete with pictures, references to "lovely girls" and "let's just treat them as objects". I noticed someone got up and walked out at this point.
In other fields such as technology, some conferences have found it necessary to develop a Code of Conduct to spell out appropriate behaviour for people who need it spelled out; e.g. here's an excerpt from PyCon's:
All communication should be appropriate for a professional audience including people of many different backgrounds. Sexual language and imagery is not appropriate for any conference venue, including talks.Meanwhile over in Vermont, the Gordon Research Conference on CADD was talking place at the same time. This particular meeting had a focus on the use or abuse of statistics with a goal to improve the situation. The thing is, GRCs are subject to the Chatham House Rule. Before I checked the Wikipedia link I thought that this meant that everything discussed at such a meeting is confidential, and I think this is the common understanding (see for example Peter Kenny's reference to this over at his blog). However, apparently it simply means that the discussions must not be attributed to anyone. Either way, probably more people misunderstand the Rule (like me) than understand it.
Be kind to others. Do not insult or put down other attendees. Behave professionally. Remember that harassment and sexist, racist, or exclusionary jokes are not appropriate for PyCon.
Attendees violating these rules may be asked to leave the conference without a refund at the sole discretion of the conference organizers.
I understand that this may be out of the control of the organisers, but it seems to me that this rule holds back the communication of the information to a wider audience: can you tweet the talks? can you post the slides? can write a blog post about the conference? can you even mention it to co-workers at coffee? Do people really present controversial work that needs protecting by the Rule?
I guess what I'm really asking is, could everyone just follow Craig Bruce and Peter Kenny's lead and post their slides on Lanyard already? (Just don't mention the Rule) :-)