A and B are going to take a bomb-defusing class tomorrow.
A: I am going to dominate that class. You don't cross-stitch for 20 years without developing a steady hand.
B: Wow, you really think that is a brag, don't you? 20 bucks says, I do better in that class than you do.
A: All right, you're on.
C is super drunk and A is offering to sober her up.
A: I got this. I'm a master at sobering up.
B: Are you sure?
A: Uh, you don't go to the Renaissance Faire every weekend in your 20s without learning how to handle your mead.
B: Great. Thanks, C
I hardly understand what these marked sentences mean. I definitely don't understand the construction, though. Why do they use "don't" here, not "didn't" or "haven't" ?
Those dialogues was taken from an sitcom.