DH and I must be very lucky, we laugh out loud many times a day.....of course it may be that we're just easily pleased
DH didn't have much of a sense of humour when I met him, but his parents had both had a sense of humour bypass, so that wasn't surprising!
However, I grew up in a family who could see something funny in almost everything, we were all arch gigglers, and after a few months DH had learned to laugh until he cried!!!
I suffer with clinical depression, often have to force myself out of bed in the morning, and sometimes just can't see any point to anything at all, but then something makes me laugh and I'm fine again!
I do think some folk lose a bit of humour as they age, I know my mum did, maybe things irritate us more as we get older........but I intend to laugh all the way, life's far too short to be taken seriously