I approach decals like I do tattoos I suppose. Very much less permanent, but I generally look at them and wonder if I'll still think something is funny/cute in a year or two. Sayings and phrases fall short of that, but I'm considering buying this one:

Minus the text. I've made basically this image in colour for a sign on my daughter's wall, without the text. It's one of her favourite BT21 characters. The moon is a wooden sign from the dollar store, I just painted it over and added the cardstock Koala to it.

Asides from that, this decal gave me a laugh.

Other than decals, I love seeing personalised license plates in the wild. I wish I had photos of some of the ones I've seen, I've seen a few that were actually really funny, or interesting. I don't have any examples though.