Just kidding, just kidding. It can't be farts, farts are gross.
Might be fresh-baked bread, that's pretty dope. Any sort of meat that's been stewing all day, then you walk into the house and it smells like a fat wall of yummy, that's good. I like the way it smells outside after it rains, or the way it smells inside after bacon.
I like the smell of my wife's pillow. Wow. That came out way nastier than I meant it to. No, wait, I read it again. Now it sounds super creepy. Uggh.
I kinda like the smell of my own balls. Is it that weird?
Then there's the you shouldn't be smelling it category, like sharpies, gasoline, glue, the palm of a stranger's hand, inside of a dog's ear, old mittens, hot rubber, burnt hair that's been recently peed on, and so on.
Wait. Is this a riddle? Like was I supposed to understand something inherently about this question and have a witty response?
I got it. Whale shits.
Short Answer: Whale shits, coincidentally, is the favored pet name of my smelly-pillowed wife.