Why Can't We Be Friends?

Think about this for a second.  How do you make friends? 

I had to think about this the other day while turning down, yet another, proposition for a friendship.  I know I sound pretty mean, but it’ll all make sense in a moment. 

Here’s what I’ve narrowed making friendships down to:  a shared experience, friends in common, common interests thus leading to a good conversation, or close proximity/frequent encounters.  Have I covered all the bases?  I hope so.  Here’s a somewhat common exchange with me in Uganda:

“Good afternoon,” an older Ugandan man on a taxi says to me.
“Good afternoon,” I reply.
“Well done,” the Ugandan says, thanking me for my work, (a habit influenced by the mother tongue).
“Ah, thank you, you too,” I reply. 
“So, you are from which country?” He begins, with a long string of predictable, and on my end, well rehearsed questions.
“America.”
“Ah, how is Obama?”

...and so it goes...and after some time, we arrive at this point--
“So I would like to be your friend.  Can I get your contact?” 
At which point I’d really like to say, “Why, so you can call me at 1 AM when your phone calls are free and ask me 100 questions about how to get to America/how to get a sponsor/how to marry a mzungu?  In reality, ssebo, we have nothing in common enough to talk about, so no you cannot have my contact.”  But that would be kind of harsh.  Instead I just make jokes and avoid giving them my number until I get out of the situation. 

My question to people everywhere is, is this a natural way of making friends?  You strike up a conversation with a complete stranger, make small talk and then state that you would like to be their friend.  Personally, I can’t think of any friend I’ve made by stating that I would like to be their friend--it just happens.  What I’m really wondering is, do Ugandans make friends this way, or is it because I’m the mzungu?  I’m almost positive I know the answer to this, but I still feel bad when I turn people down for friendship.  It just sounds mean.