What are the differences between tomar un taxi y coger un taxi?
I heard about it before that Coger has bad meaning and better not say it, but I have no idea why it´s bad ? In dictionary it doesn´t have bad meaning.
Or maybe in some other countries that mean bad meaning? What does it mean in bad meaning?
En España significa exactamente igual "coger un taxi" que "tomar un taxi".En lenguaje de la calle,se usa más "coger un taxi".
En Latinoamerica ,"coger" es una "swear word"
Melissa, it means the "F" word 
From my understanding, Spaniards use it to mean to "catch" a taxi, while most Latin Americans would laugh, wondering why they would want to f*** a taxi, if you catch my drift.
So to answer your question, tomar un taxi would mean to take a taxi, but coger un taxi would mean to catch a taxi, which is actually different, I'd say. But if I was in Central or South America, I'd opt for saying tomar! Hehe.
I coger taxis and buses on a daily basis in Bogotá and have never received the slightest titter for having done so. One can coger and recoger here to one's heart's content sin problema...
To be fayre, 'take' can have sexual connotations in English too, it all depends on the context and its obvious accordingly.
Here, tirar pertains to the sexual act and so one has to lanzar dados.
People look at me oddly when I refer to a cigarette as a fag, totally normal in British English.
I always laugh when recounting the tale of my friend's father asking an American Airlines stewardess if there were any loose fags on board...
In Spain you can use coger un taxi or tomar un taxi ...they are both acceptable although coger is more common. However, in some Spanish speaking Latin American countries such as Mexico coger is a rude word and should be avoided at all costs!.
I have recently learnt that coger is acceptable in Columbia from a native Columbian girl (whom I have successfully encouraged to join SpanishDict). She told me that her (native) Mexican friend told her that coger was a bad word and should not be used especially to ladies.
I am sure that Lazarus is right and coger can be used in some Latin American countries. I believe that Peru (my country of birth) is Not one of them and tomar is used instead!
I hope this helps 
Just a cultural difference. Nothing else.
Please remember you can use the Search button in Answers to check previous threads before making a question, just in case someone has had the same doubt.
Here ´s an example. Check this thread
I always laugh when recounting the tale of my friend's father asking an American Airlines stewardess if there were any loose fags on board...
omg...
Is it a very serious, very bad word? What will happen if I said it not on purpose? Will they beat me up??
Don't use "coger" in México anyway, tomar will do fine. All other forms of "coger" are ok.
Follow the link in mediterruno's answer for a lot more on this.
In Ecuador, coger is fine.
I thought that coger was offensive only in Mexico.
Pillar un taxi.