Thats right, I seriously am going to make a thread devoted to jokes about math. Yes, I am an incurable nerd, thanks for asking.
Its not my fault, I have 2 math classes this semester, both with quirky professors who like to make strange jokes, I pick these things up and felt like torturing you all with them, lol.
I'll have more later, but for my first trick, I'll prove that 1 in fact equals 2.
lets say we have 2 variables, a and b, and they are equal, so;
a=b
we first multiply both sides by a
a^2=ab
now we subtract b^2(b squared) from both sides
a^2-b^2 = ab - b^2
now we factor both sides to get
(a+b)(a-b) = b(a-b)
and we then divide both sides by (a-b) to cancel that out which gives us...
(a+b) = b
and since a = b we can substitute for...
(b+b) = b
or...
2b = b
or...
2=1
So there you have it, 2 equals 1, up equals down, and the universe doesn't exist. (extra points for anyone who figures out the flaw, lol)
Later I'll prove that -1 = 1 and put up a more traditional 'joke' my teacher told us, but now I have to go to Math class

.
Even though I know no one but me finds this stuff funny:
"I wish I were you derivative, so I could lie tangent to your curves."<-best(calculus based) pickup line ever