Bench Etiquette

I'd like to think of myself as a (reasonably) polite person.  Perhaps I am overly sensitive at times, which is why I'm asking the question about bench etiquette.  I could be behind the times.  (Am I turning into a fussy old lady?  Please tell me no!)

The scenario is as follows.  At the office complex where I work there are two picnic benches in the back of the building.  They are in the direct sunlight.  This is also the only place people are allowed to smoke.  Towards the front of the building, near the road, there is a shaded area with a bench.  This is area also overlooks the building to the north which is currently under construction, so it can be loud in the area as trucks go in and out and all sorts of equipment is being used.

When the weather is nice, I try to get outside.  Sometimes I walk, but sometimes I like to find a place to sit and just read my book (ok, officially a Nook, but...).  I generally gravitate to the front of the office where the bench is in the shade of the trees.  If the bench is occupied by someone else or a group of people, I usually head to the back of the building.  The picnic tables there are rarely used.  It's a nice area, but it can get hot (no shade); I don't mind the smoking too much because there isn't that much going on and the tables are in a place where the smokers generally aren't.

On a recent nice, not too warm, day I went out at lunch and found the front bench unoccupied.  I sat on the right hand side of the bench, with my purse to my left.  I dug out my Nook and glasses and started reading.

Five or ten minutes into it, three ladies (girls?) came by.  They were speaking another language (I won't say which one so as to prevent any discrimination), but I know they also speak English.   They said nothing to me, but "took over" the bench.  They chattered away; I don't know about what.  They never addressed me. And perhaps I was rude in not addressing them.

I "thought" the appropriate etiquette if one wanted to share a bench that someone was already seated on was to ask if it was all right.  I have done this in the past and when I've sat on this bench before and someone wanted to share it, they asked if I minded.  (Which, of course, I didn't.)

I did feel a bit uncomfortable sitting there as they chatted and giggled.  But I wasn't going to move.  I continued to read, or tried to, for another 10 or so minutes.  Then I decided it was time to go back inside.  But I wondered, would I have stayed outside longer if my space hadn't been "invaded?"  Next time I go out, will I avoid the bench?  Will I go straight to the back of the building where the picnic benches are even if it is hot?

Am I being overly sensitive?  Am I over thinking this?  What would you have done?  (Or not done?) There's still plenty of outdoor time left before it becomes too cold; let me know what you think!