A new study published in the Journal of Experimental and Social Psychology, shows that men literally go stupid when talking to attractive women.  http://www.telegraph.co.uk/hea.....to-pretty-women.html
The joke of "thinking with the other head" is correct.  The men in the study performed significantly worse on cognitive tests while talking to attractive women than they did chatting with people they did not find attractive.
Conversely, women are not affected in the same way.