It's commonly called the Miami Hurricane rule. It is to deter players from drawing attention to themselves. In the 80's & 90's Miami was notorious for a player removing their helment after making an interception, fumble recovery, qb sack or touchdown. It started happening too often with every team and the NCAA ruled it as unsportsmanlike conduct and a 15 yard penalty.

over celebration u can after u get off the field though

or it can be used as a weapon...

Because too many jacknuts were taking their helmets off and running around the field flexing after routine plays...

The NFL (and NCAA) were trying to get some class into the game...

It was really bad about 5 or 6 years ago... guys where making a tackle after 10 yards, ripping off their helmets and running 50 yards as if they had just cured cancer... I am all for celebrating, but it was just getting ridiculous...

becuz its considered showin up the other team

It's for showing their ugly mugs.

Same as taking off your gloves in hockey.....means you are ready to rumble.