Solution to 12A has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Excessive consumption of alcohol in big dinner parties by star (5,8) BINGE DRINKING {BIG+DINNER}*{KING}
8 Martial arts instructor's endless wisdom (5) SENSE SENSEi
9 Macho male is perhaps taking special pleasure in being dominated (9) MASOCHISM {MACHO+M+IS} over {S}
11 Growing trend of crash dieting is primarily ridiculous (6,4) RISING TIDE* {DIETING+IS+Ri...s}*
12 Stand by one breaking down on retirement (4) ?A?S (Addendum - DAIS {SA{1}D<=}- See comments))
14 New jockey crushed by mistake, getting more jittery (7) NERVIER {N}{ER{VIE}R}
16 Confront prince - chucked cup of tea angrily (7) OUTFACE {CUp+OF+TEA}*
17 Clear the dirty boxes connected electrically to the ground (7) EARTHED [T]
21 Horseman terrified to tackle rebellious Italian mount (4) ETNA [T<=]
22 Not lucrative to maintain university for bird-rearing (10) AVICULTURE {LUCRATIVE}* over {U}
25 Male star playing lead in Chinatown as a clever dick (5,4) SMART ALEC {MALE+STAR}*{Ch...n}
26 Good deception, snaring Dravid at first slip (5) GLIDE {G}{LI{Dr...d}E}
27 Reason to visit trichologist leads to quibbling (4-9) HAIR-SPLITTING [DD]
DOWN
2 Device improving air quality inside - infection is eradicated (7) IONISER [T]
3 Endlessly kiss lady in darkness? OK! (5,5) GREEN LIGHT {GREEt}{N{L}IGHT}
4 Resign from department over issue (5) DEMIT {D}{EMIT}
6 High boot (4) KICK [DD]
7 One enthralled by knocking back drink at a Japanese city (7) NIIGATA {GI{1}N<=}{AT}{A}
8 Eccentricity of one on dope, overwhelmed by tension (11) STRANGENESS {STR{AN}{GEN}ESS}
10 Outstanding work by team with precise moves (11) MASTERPIECE {TEAM+PRECISE}*
13 Error found in minute - it will brighten things up! (5,5) STRIP LIGHT {S{TRIP}LIGHT}
15 Rebuild deep love, making up after a little rift (9) REDEVELOP {DEEP+LOVE}<=>{Rift}
20 Escape in mounting commotion, stealing large carbuncle at centre (7) ELUSION {NOISE<=} over {L}{c..bUn..e}
24 Wanting a set of steps for song and dance (4) STIR STaIR
Reference List
Special = S, New = N, Prince = P, University = U, Good = G, Lady = L, Department = D, Victory = V, Dope = GEN, Gun = GAT, Large = L