This is because it is your farts.
The scientist has found that most people like smells that they know well. Some examples are Grandma’s homemade apple pie baking in the oven, certain laundry detergents and fabric softeners, the cologne Dad always wore when he and your mother went out, the smell of gasoline and oil when Grandpa was out in his garage working on motors. We like familiar smells. It is no different when it comes to our own peculiar odors. Your own farts is surely a familiar smell for you. That would be the real reason.
Although it is normal for us to possibly like our own smells and even, to others, our disgusting stenches. We normally do not like other people’s “stenches.” Things that smell bad to us are usually bad for us. Maybe being ok with our own bacterial properties (farts are bacterial) is ok but we tend to stay away from other people’s because maybe our body is keeping us safe from something bad like an infection or illness.
REFERENCE: http://www.sciencealert.com/watch-why-do-we-like-our-own-farts