The ornamental design for a drop down trailerhitchx, as shown and described.
FIG. 1 is a front and right side perspective view of a fixed drop down trailer hitch X showing my new design;
FIG. 2 is a right side elevational view thereof;
FIG. 3 is a left side elevational view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a bottom plan view thereof;
FIG. 6 is a rear elevational view thereof;
FIG. 7 is a front elevational view thereof; and,
FIG. 8 is a front and right side perspective view of the fixed drop down trailer hitch X with related environment in broken lines. The broken lines form no part of the claim and are shown only as relatable environment.