In Linden's version of "So You Think You're Tough?"(minus the headgear,boxing gloves,mouthpieces and as far as we could tell,protective cups) a young golfer emerged as the Toughman. Thomas Johnson,18,the current Ft.Lewis Amateur Champion and a Linden member shot 78 on Saturday to win this year's Toughday Competition. Formerly known as "Dave's Ball Buster"this format is identified by a course set-up that can only be described as "heinous".In Boston they would call it "wicked hahhd".In Mexico City(or Phoenix,for that matter)they would…