Maddux is on the right track suggesting a big jump with the "angel" mutator. I've got some additional tips that should help, though.
For quickest results, start a custom game on Goat City Bay with the Angel Goat mutator turned on.
There are several high points on this map you can start from:
- The wind turbines, which are high and on the right from where you start
- The dam, which is high and to the left from where you start
- The roof of the big hotel down by the water, you can enter through the front and take the elevator to the top, where Deadmau5 is holding a concert
From one of these places, jump off towards as much land as you can - it's critical that you land on the land and not in the water.
Now, hold W, A, R, and the right mouse button and you ought to start doing one super, super long trick. If you need to adjust your trajectory, release the right mouse button and use W/A/S/D to move yourself. You can release the R button for short periods to increase your downward momentum, if you've been in the air for too long. Just make sure you're holding it as you start to land.
As you get close to the ground, release the right mouse button while holding the rest (W, A, and R). This will auto-level you so that you land on your feet. If you've been in the air tricking long enough, you shouldn't need to do any other combos. One jump was enough to max out the score totals for me.
That's 143 million points, with no combo bonus or anything. Presumably you could get some insane points by kicking your way through a house or shop, or doing a wall run or some additional tricks of some kind. It's completely unnecessary, though.
If you want even more points, lick one of the following objects:
- The Wind Statue, which is on top of the middle wind turbine at the wind farm
- The "42" towel, which can be found by jumping down from the roof of the hotel, towards the water. It's on the edge of the pool on the ledge midway down the side of the hotel.
- A whale, which you can summon with R once you've taken the 42 towel to the alien ship high above the dam
If you're actively licking one of these objects while you do your tricks, you'll get a bonus, just like you did while licking Goathenge in my previous answer. There are likely other things that would qualify, but these ones are easy to describe.