To be pissed off that when DS did well in his GCSEs FIL said this...

[Nanacuddles]

DS got 3 A*s, and 11 As which I was so proud of, I think he's done fantastic.

However, when he went to his grandad's house (DH's dad) he walked in and said 'I've just popped over to show you my results' and his grandad said 'Well you won't have done as well as Ellie, Anne's daughter, she got 9 A*s'.

Totally pissed on his chips.

This is mean, no?

Miserable old git.

Tell ds CONGRATULATIONS, he has done brilliantly! And point out that grandad is starting to go a bit ga-ga and isn't it sad?

Had to re read OP, can't belive he said that to DS's face, how horrible- is he usually mean like that?
congratulations to your ds, hope he enjoys celebrating!

Your FIL is being an idiot!

Your son is obviously a very bright, hard working lad and has done tremendously well. You must be incredibly proud

Well done to your DS. Your FIL was very mean he should have congratulates him.