Up until you tilt the cup and the whole thing slides off..

The purpose of the domed lid is to already do this, and if you put it on the right way it will hold almost as much, generally without the danger of a slurpee to lap incident.

Steak and Shake (A southeastern burger chain known for steakburgers and... something else, I can't quite remember.) used to use thin pressed styrofoam cups for their shakes. If you hit it wrong it would split on the horizontal axis, along the cup instead of vertically.

One night after a miserable day at work, I stopped and got a vanilla shake as a bit of a treat. I had one sip as I was pulling out of the parking lot and put it in my 'cupholder' (Old Beetle, had no cupholders, so I'd stick it between my legs. Generally safe.) and when I turned out of the lot, some asshat came down the street the wrong way, so I had to slam on the brakes. And since it was a manual transmission, I had to hit the clutch at the same time, so both legs were extended... which snapped the 20 ounce cup off about two inches above the bottom.

Snowballs.

Heh. That's why I told the story. "If you can't laugh at yourself, make fun of everyone else." :D

And from the original post, I hadn't actually noticed that it was a tiny cup and large lid, so the cost/benefit might be worth it.

Snowballs! I've done that a time or two. I'll have to remember that.

I love Steak n' Shake! Their garlic burger is fantastic, but unfortunately, where I live, we only have a small one in the mall which has a limited menu of both burgers and shakes. I gotta go to San Antonio to get the garlic burger.