The worst one we ever had was "build a model of your house. Be as accurate as you can".
We'd moved house less than a week before, from a square, like everyone else lived in, to a 300 year old hodge podge of buildings that someone had joined together randomly.
I informed dd (primary 5) that she could do a square and pretend that we still lived in our old house, but that wasn't good enough for her.
She built an amazing, fairly accurate model, using 6 boxes glued together, and gallons of sellotape, paper mached it, marked windows and doors (all of which I had to cut so they opened the proper way), and basically spent the entire half term (and a lot of tears and tantrums) on it.
She's now left that school, but it's still on display in the foyer, and every time I see it, it makes me feel sick, and reminds me of that hellish holiday. I told her teacher that next time there was homework like that, dd wouldn't be doing it. And she never did.
However, in Scotland at least, you can opt out of homework at primary level really easily, we did for most of P7, due to going through a majorly tough time, and really not needing to worry about homework. And, to be honest, that sort of homework is just crap.