based off phrases from not only South Park but Spaceballs as well.

Blatently obvious. If a fat person tries to sneak round a corner they will be seen, as their belly will protrude first and give them away. Hence if something can be seen a mile off, or is really obvious, it can be 'seen coming like a fat man round the corner'

said by cool people who have a lot of minor inconveniences in there life 😘