I gotchu.
When you detailRP, try to describe features of your character, or how they appear / look DOING the thing they're doing. You also try to make the action seem as vivid as possible—even if you are describing minute/insignificant things. DetailRPing is similar to imagery in a book. Or, if you do it wrong, it would just be pure slop.
An example of a vague action:
John Doe punched the Berry Allen impersonator in the face. -> Sure, in non-P2L combat, this would be a good action. But if you want to DetailRP (Usually for P2L in this scenario, you have to describe what he is doing before and after the punch (without double-actioning) and how the punch looked, and felt, and what would happen if it connected)
A better action would be:
John doe licked his lips, quickly winding his arm back, and landing a clean punch to the kid in the flash suit's face, causing a sharp tingling sensation, and throbbing ache, as well as immediate redness if the hit landed. John then smiled, and shook off his hand, a sharp pain shooting through his knuckles. (The 'if the hit landed' part was courtesy, and means that there is no PowerRP going on.)
Why is this better though? Firstly, it adds some more detail to John's punch, and describes the effects of the punch, what John Doe feels after, and what he does before. But this is still not perfect.
An even better action would be:
John Doe licked his lips, the coppery tang of his own blood overwhelming his senses. He hadn't noticed his broken nose, which was starting to throb. His eyes widened, and he stared at the Flash impersonator, glaring daggers at him, his Jade eyes so filled with rage they looked like they were going to pop out at any second. He took a breath, wiping the blood off his face, before quickly winding his arm back and shooting it at the Flash Impersonator's cheek. His fist would connect with a sharp crack, causing the Flash Impersonator to feel an immediate throb in his face, which would be sore if the hit connected. He pulled his hand back, shaking the pain out, which came in waves. 'Tch' he muttered, his knuckles bloodied and bruised.
This action is (of course) not perfect, but paints a way better picture. There is a ton of information provided on exactly where his fist hits, and the effect of the punch. It also is very vivid, and describes smell, sight, feeling and uses forms of descriptive imagery to really fluff up the action.
I bolded the parts that make the attack dodgeable (for some reason)