Periscope

When an individual discreetly checks out someone they deem desirable or attractive.
Emphasis is placed on viewing the individual without being caught. Similar to how a submarine would use its periscope to view a target without being discovered.
Those versed in periscoping are exceptional at situational awareness. They are able to enter a room and quickly identify the most attractive individuals without being caught.
Direct staring is considered a novice technique. Advanced periscopers will utilize mirrors/reflective surfaces to view their targets.

Did you just periscope that girl man?