How can I interpret the intent of and respond to cars behind me honking?
Broadly, not a lot. Legally it's probably technically unlawful on several grounds (horn not used as a warning device, causing alarm, loud noise, possibly harassment), but they're all petty offences and unlikely to get a useful response from Police. If it happens in front of a cop they might pull the motorist over for a chat, but that's unlikely.

My answer to "Is there a polite way to take the centre of the road without antagonizing motorists?" might be helpful as it has links and some anecdata.


  In my experience, no. The problem is that however polite you try to be you're taking the lane so you're in their way.


My suggestion is that you clearly take the lane (being assertive makes harassment less likely) and use daylight-bright rear lights. The lights are fairly affordable (see Nathan's bike light database) and I find they do help.

Going faster will help, if you can match the speed of the other traffic. Since most cyclists can't do that, going faster just makes your life less pleasant. And slightly more dangerous, because "the faster you go, the bigger the mess" (NZ and Ireland anti-speeding campaigns, both feature graphic images).



And to address gender since it seems important to some people: the evidence is mixed between "no affect" (Queensland, Oz) and "women get treated better" (the UK Walker study). Here're some typical quotes:


  Of 1830 respondents, 76% of men and 72% of women reported harassment in the previous 12 months. 


(Queensland)


  {overtaking drivers pass closer to cyclists} when the rider wears a helmet, rides away from the edge of the road, is male, or when the vehicle concerned is a bus or heavy goods vehicle. 


(UK)

One thing to remember is that the differences Walker found were small - 1.35m vs 1.40m passing distance. There are other studies, once you're past the first page of this google search it gets interesting.

This report cites references when talking about passing distances and how far from the curb you should ride, and talks to police and cycling advocates:


  As cyclists we should be confident in taking up as much of the lane as we feel we need to in order to be safe. At a minimum we should ride 50cm from the curb but we should be confident in using more of the lane if the conditions dictate it — as a result of roadside obstacles, upcoming intersections, narrow lanes, potholes or any other factors.