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3.
Investigators, private detectives, spies, others who act for the government including telecommunications workers WHO wear baseball caps with video and recording devices secretly (or not so secretly attached). Generally they walk around looking totally disinterested in anything and rather gormless, a total giveaway!
I noticed a couple of guys walking up and down outside my house wearing baseball caps, then one of them started talking to the small microphone on the cap. Very strange behavior! Either he was a wacko or rather nosey.
by THE ENHANCED July 11, 2011
 
1.
Device which, when fitted to the head of anyone driving a car, immediately removes any concern they may have previously exhibited for their own, their passengers, and, well, anyone elses safety.

Especially effective when driving 'modded cars'. See kev.
Tracy thinks that Trevor's baseball cap makes him a much better driver.
by Gabba March 05, 2004
 
2.
Device used to notify others that they are in the presence of a dickhead. The point may be reinforced by the wearer displaying said item at alternative angles, particularly back-to-front especially when facing the sun.
That wanker in the baseball cap.
by redroar August 22, 2004
 
4.
A Type of hat generally worn by old men ranging from 75-93 years old. Wearing a baseball cap is a sign of ageing and usually paired with dependency of prescription drugs such as CRESTOR or LIPITOR . In very rare occasions used by mid twenty year old woman with drawers full of baseball caps and shades to express the excitement of a return to California on Instagram or other social media.
"In moving back to CA you recognize the importance of having an entire drawer designated to baseball caps & Sunglasses (insert CA related Emoji here)
by THE BASEBALL CAP GUY September 24, 2014