I'm not particularly good at giving criticism myself. Usually you'll just get a "Yep, liked it." from me. It doesn't add much towards the sketch itself. But I'd like the writer to know they "did-a-good" and that their on the right direction to a collection of decent sketches.
I sometimes suggest alternative lines or punches. But feel like I'm stepping on toes. So unless it's requested, I don't normally bother.
If I don't "get" a sketch, I think it's good mention it. As they'll get an idea of its demographic. Not the most important thing. But in my example, a lot of topical sketches will go over my head, whereas mixing it with slapstick or whatever humour I understand, you'll get an extra viewer - if that's what's wanted.
And it was just a joke?! A parody?!!
Although, I'd of included more puns 
