This rule should apply to all sex, at any time, in any place, but it's particularly important to consider during a threesome. Just because she's agreed to have a threesome, doesn't mean the regular rules go out the window. Be respectful of her preferences, and please, don't start speaking as if your name is Lex the Giant or Dick the King. Have some originality.

Remember that the woman or women involved are people, not pleasure toys. Threesomes have limits too, so it's important you proceed slowly, listen carefully, and pay attention to her needs, both spoken and unspoken.