Someone who does what is required of them. Usually this refers to duties in a group task or work environment. Best compared to some one who is a slacker.

Making your best effort

to work as hard as other people in a group

v.To do a good job of a hard task. To achieve something beyond your capabilities

when a man had a dick bigger than 1 1/2 feet

It means someone who can actually do what they’re supposed to, they meet the expectations and do their job