Why would you say this? Do you hate your children? What possible filter could you pass this thought through that still allows this thought to come out of your mouth? The only reaction to this piece of advice is for the PTB to die a little inside and possibly shed a little tear on the outside.
"Say goodbye to sleep"
We all sleep. Sleeping is universal. Sleeping is awesome. No one doesn't sleep. So why, even if it was true, would you tell someone that they can say goodbye to sleep? It's the ultimate kick in the pills. This is literally the adult equivalent of telling kids Santa isn't real.
"It's like watching your favourite pub burn down"
First of all with the rate pubs open, close or change hands these days who really has one "favourite" anymore? Secondly, except for alcoholic arsonists who has ever watched their favourite pub burn down? Lastly, who could possibly equate the image of a building going up in flames to the birth of a child?
If you really want to use imagery to describe the birth of your child try one without the presence of fire or alcohol.
"You probably shouldn't eat/drink that"
I guarantee any PTB cares more about the health of their growing child than you ever will so it's more than likely they're fully across what they safely can or can't consume.
And to the barista who suggested my wife drink decaf coffee instead of her normal skim flat white, your advice that coffee "is bad for the baby" was only made less welcome by the fact that after you offered it, you then took a smoko break.
In reality, when a PTB tells you they're expecting and asks "Any advice" your first/only answer should be "You'll be fine" because a) it reminds the PTB that people all over the world have children and raise them every day in circumstances worse, better or the same as theirs b) it relaxes them and c) YOU'RE NOT AN EXPERT ON PREGNANCY!!!*
*Unless you actually are an expert on pregnancy in which case you're probably unlikely to be dolling out free pregnancy advice to idiots like me on the street.