  I realize that to the casual observer,  I might seem like a typical,  bachelor male with no cooking skills or grocery store experience.
 This would be one of those times when judging a book by its cover would lead one astray.  So when the lady ( i'm sure she was very nice and trying to be helpful)  took my squinting through a blinding headache that almost had me in tears as i tried to read the can of tuna I was holding for being confused by all the tuna choices,
 and decided to help out a clueless boy by giving me unsolicited advice on the particular can I was looking at,  saying,  " that one has a really nice flavor"  I just nodded at her and hoped she would go away and leave me to my pain.  She did,  or so I thought.  not 3 seconds later she comes back to tell me that that kind of tuna is packed in olive oil,  so I didn't need to get mayonnaise too,  I wanted to tell her that I know what the f*  tuna packed in oil is lady,  and if you don't leave me alone,  the hopscotching elephants in my head are going to gain the upper hand,
 and I will be writing on the floor trying desperately to keep my brains from oozing out of my ears,  prompting some underpaid kid in a Hawaiian shirt to have to mop up something really gross in isle 3.  instead I grunted and nodded.  there should be some sort of sign you can wear when talking to another human is just too much for you to muster,
 and everyone would know to leave you alone.  maybe it could say " Normally I would be happy to talk to you.  But right now I am having a personal emergency,  I didn't get enough sleep last night,  i am in terrible pain,  I am cranky,  I am hibernating and i only got up to forage for berries and you are standing awfully close to my newborn bear cub,  or I really just don't feel like engaging in anything more than the absolute minimum interpersonal interaction I can get away with right now.  Thank you for your understanding,  and please try again when this sign is not being displayed.
 It would have come in handy when,  minutes later,  the underpaid kid in the Hawaiian shirt ringing up my purchases asked me for my zipcode.  All I could mutter was " i'm not from. no. i don't know"  and he replied " Brookline?  to which I should have just nodded and grunted.  but instead I said " philadelphia. just. I. use brookline"
