Valve float is when the cylinder valves are unable to close completely between cycles, usually due to high RPMs beyond the engine's design, but possibly due to very high mileage, often well beyond 100-150k miles. This meme refers to the former.

Longer, more detailed explanation:

Internal combustion engines use something called poppet valves to control the flow of fuel and exhaust into and out of an engine cylinder. A poppet valve is generally a disc shaped, tapered plug atop a longer shaft called the valve stem. The stem runs through a stout spring, then through a hole in a disc attached toward the bottom. Valves are opened by being pressed by their stems, popping up toward the cylinder chamber to open whilst compressing their springs, then being released so the spring can push the valve closed again.

If an engine is driven to rotational speeds beyond its design, the springs may not have enough compressive force to fully control the valves. The valves begin to 'float', where they can be bounced open, opening too far, then are unable to completely close before being bounced open again. This can cause a number of issues, ranging from power loss to catastrophic failure. In high performance engines, this is prevented by stronger springs paired with a stronger, more precise system capable of handling the force required to open them.

The meme is describing someone presumably driving a shitbox car pushed well past its limits to ourperform a high performance vehicle. It's definitely an exaggeration as most vehicles would break well before producing that much force.