"darn tootin fun" originates from an episode of the popular sitcom "Friends" which teens today love.
Son: Hey dad I'm kinda bored, you wanna do something?
Dad: I'm feeling DTF
Son: Alright let's go get in the hot tub!
Dad: Maybe I'll even let you taste my cum!
Son: Really? Coke and rum?
Dad: Yeah... sure
Friday night: Jimmy - Lads who is DTF tonight.
Sean - Sorry guys I have sand in my vigina and can't come out (hence not DTF)
Everyone else - I am way DTF (displaying an extreme level of DTF, hence is willing to go out, drink alcohol and try to pick up birds)