In the poem, "red squiggles out" when we have a cut on our hand. The word "squiggle" is interesting; it describes an irregular, curly line of blood emerging from the wound. Perhaps the blood is "squiggly" because it follows the lines on our hand. The poem doesn't say what happens when we get a deep cut, but we assume that the blood doesn't just "squiggle" out; as my colleague mentions in her answer, a deeper cut can cause blood to gush out in greater volume.
This leads us to what the color red means to the poet:
Red is a shout
Red is a signal
That says, “Watch out!”
The color red warns people about danger. It's a bright, attention-grabbing color. In the poem, the color red can spell sexy (as in a woman's red lipstick) or beautiful (as in a red rose); it can alert us when someone's angry (as in red-hot angry), and it can also spell danger. So, the color red can signal at different times anger, danger, beauty, or sexiness. Additionally, when people become emotional, the poet tells us that "Red is hotness/ You get inside/ When you’re embarrassed."
Here, the color red explains how someone feels. Some people blush when they get embarrassed; the little twinge of red on someone's cheeks alerts us to how that person feels. The poet says "Red is the giant-est/ Color of all." That's the impact of the color red. It's a "show-off,/ No doubt about it," perhaps because it knows how important it is in our lives. The color red causes us to react to what we see and feel. Its power is felt daily in our lives, so much so that the poet invites us to imagine what it would be like to live without it.