Thank U and Mention Not!!!!!

i had this experience while returning from my college by TamilNadu
Express..i was sleeping in my berth while at vijayawada somebody woke me up and requested me to shift berths as there was a girl with him and she couldnt climb up ( that idiot shifted me to the upper berth).. as kind-hearted as i was i immediately obliged.. the girl thanked me for that and as was my custom i acknowledged by saying "Mention Not" and then came the funnniest part!! she looked at me preplexed and asked me to repeat what i said..i think she couldnt get what i said or she was not used to mention nots!!!! this caught me offgaurd and made me sit up and think in the middle of the night as to the correct reply for a "Thank U".. i spinned my grey cells or what was left of it after a tedious week after project to research a solution (best possible) for it....well in my research i found that different people prefer different acknowledgments for that word...
these are some examples :
well a Briton of High Class will say "Its a pleasure" when he is confounded by this word that too by a beautiful Lady.and any ordinary Briton would say "Mention Not" for a reply and that
was what we had been drilled to say in our primary..our English Teachers Mrs.Kamakshi and Mrs.Sulochana had drilled us like anything to say "mention Not" whenever somebody said Thank Q.. and we were supposed to practice saying it among ourselves while we borrow something or my friends to do some favour for me..
well coming to the next country the Americans usual word of ack.. would be "u r welcome" or "anytime"...now coming to the desi version..we indians are habituated to saying "No Problems" or to put it in the words of today's youth "No Probs"!!!!. well
as far as my knowledge goes No probs or No problem for that matter is said whenever some say "Sorry"...but only in India u find the same reply for two different queries and that too when the queries are poles apart..well i just managed to say NO PROBS to that girl for which she presented me with a very beautiful smile of hers in the middle of the night..but i'm still confused as to what should be said ??? and now i have this big concern about where the language is going in this cul-de-sac of hip and hop world of today..."QUO VADIS ENGLISH"....well is this concern a futile one in a land where there is still some alienation towards this foreign language???