Pussy boy legs is a slang term used to refer to a weak pair of legs. If someone has "pussy boy legs" they tend to have absolutely no lower body strength. This can impair them from running, jumping and other leg based activities
Example 1:
Shay: I forgot to work out today
John: Make sure you don't get Pussy boy legs
Example 2:
Shay: I'm gonna kick the shit out of you
John: Not with those Pussy boy legs!