The ornamental design for a men's abstract line polo shirt, as shown and described.
FIG. 1 is a perspective view of a men's abstract line polo shirt showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof; and,
FIG. 6 is a top side view thereof.
The broken lines in the figures are for the purposes of illustrating portions of the men's abstract line polo shirt, which form no part of the claimed design.