Apparently there are some guys that have a (somewhat sexual) obsession with getting fat and getting huge guts. The want to be "fed" against their own better judgement/will by a "feeder" and there is somehow an entire community dedicated to this. I am not kidding, they have like a glossary of terms. Some examples:
ball belly - a large, nearly spherical belly
belly play - touching or fondling of another person's belly
mutual belly - touching, as in a belly bump
belly rub - the physical act of rubbing another person's belly, which is generally very erotic for both gainers and encouragers (even rubbing one's own belly)
bloating - drinking large quantities of liquid (e.g., water, soda, milk) to temporarily expand one's belly
button popping - the practice of squeezing into old clothes that no longer fit to emphasize weight gain and to fantasize about getting even larger
superchub - a super obese man (e.g., weighing over 400 pounds or having a bmi of 55 or more)
teasing - comments about weight gain or messy eating that are just playful for some but sexually arousing for others, as in, "You've become such a fatty," or, "You're my fat little piggy, aren't you?"
Apparently "Button popping" - or when an older, now-small shirt is worn and the engorged stomach popped through - is a rite of passage or something, there are hundreds of vids like this on youtube:
Same guy:
