Wi-Fi 
Apple for the teacher?   MAC
Bars at the bar   ESTOPS
Gray area?   ANATOMY [he wrote the book]
Blow off steam   HISS
Big bang cause   TNT [note lower case 
b]
Plus 
lots of interesting cluing throughout
Theme: substitute W(I) with F(I) in phrases
Angler’s daydream?   FISHFULTHINKING
Auto design now, vis a vis the 1950’s?   NOFINSITUATION
Offshore WBA venue?   ISLEOFFIGHT [with IBF, both major boxing orgs. appear]
Unrestrained Kentucky Derby entrant?   FREEFILLY [kids flick 
Free Willy] 
TESRATING:   
 
 
 Three grins = Excellent: Loved it; Two grins = Good: Enjoyed it; One grin = Satisfactory: A bit bland for my taste; One teardrop = Unsatisfying: No fun