I’m thinking the なさけなや in the leftmost column means なさけない, but I can’t seem to find any info about this anywhere or if this applies to any other verbs
An adjective ending in ~や usually means “person being the way the adjective describes”.
Please see #3 here: 屋 - Jisho.org
That seems likely, but why isn’t the sentence なさけないや?
Hm, that’s a good question! I tried to find more on it but failed. So maybe I am wrong and he is just slurring the ~い, just like you assumed?
The first thing I thought of was 情けないじゃん?
I’ve also been watching Azumanga Daioh and Osaka speaks like this, so I figured some sort of accent.
I found one of those chiebukuro q&a pages where the answerer said:
So it’s probably just “old dude in manga speak”
That sounds right, thank you!