When someone, something, or anything can be defined as either good or bad depending on what situation.
although you can say 'grannyish' you could say grannyish by putting good or bad in front of 'grannyish' so it's either the 'good-grannyish' or the 'bad-grannyish'
Saul - just won this match of Rainbow Six Siege Howard- Ah that's very grannyish :)
Another example Saul- My brother Chuck just got killed in a fire Gus- That's so grannyish :(
Grannyish can either mean good or bad depending on the situation.
That was very Grannyish