Something extremely adverse (see: negative).
The torrential rains had a megative effect on my golf game.
I hope my addition to the Urban Dictionary does not megatively affect Roy Blount's on-going efforts to be honored in a similar fashion.
Airline passengers who, upon boarding, discover that there is no overhead storage available in close proximity to their assigned seat and who then place an item or items somewhere aft of their seat, necessitating a return against the boarding flow to regain their seats. After landing, they have to fight their way back during disembarkation to retrieve their belongings.
Despite repeated pleas to "Excuse me," furrowed brows and sighs of disgust met the back-packers as they made their way aft, displacing anxious passengers eager to deplane, to retrieve their luggage from the overhead compartments.
A barrier (real or perceived) that prevents a team or individual from reaching the pinnacle of a respective sport.
Members of college football conferences that are not members of the Bowl Championship Series (BCS) are often left out of major bowl bids (see: Utah). That's a real barrier (BCS rules favor greatly teams from BCS conferences) that does not preclude participation, per se, but the obstacles are significant.
Also a phenomenon evidenced when a really decent program (e.g., college football) can not seem to make the transition to a national and/or perennial powerhouse due to self-imposed barriers. Virginia Tech, for example, fails each year to be considered in the same category as USC, Texas, and Oklahoma, teams that have won many national championships. The barrier is a failure to acknowledge and resolve internal staff issues (primarily, the offensive coordinator) which leads to a general perception by the players that they can't play at the Tier 1 level. In this case, the coaching staff has created a "grass ceiling" through which the players can not progress.