When I say I'm howling, I AM

I can't stand when people say things along the lines of "That's hilarious!" without even prefacing it with a chuckle. Obviously, it couldn't have been that funny if you're not laughing. Maybe it was mildly amusing but it certainly wasn't hilarious if you are just smiling. I smile at stupidity. That doesn't make it worth a declaration of "That's hilarious!" If it wasn't hilarious then don't say so. If nobody made a joke or even if you don't think the joke was funny, don't feel obligated to say "That's hilarious!"
Don't say something is hilarious. Show it. Illustrate your point with a chuckle, a knee slap or even just a simple "ha ha ha". The best laugh to show that something really is "exceedingly funny" is to laugh so hard you're silent (although if on the telephone, it could be interpreted as a lack of laugh). Those laugh are usually followed by some sort of noise though so that's no excuse. It doesn't have to be much. Just show that you really mean it and aren't just saying that because you're supposed to.