Solution to 20D has been deliberately left unsolved and is to be answered 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 Pen pal is upset about American leader's bluntness (5,8) PLAIN SPEAKING {PEN+PAL+IS}* over {A} and {KING}
8 Calls topless escorts (5) RINGS bRINGS
9 Miss Japan picked up by champion in American club (9) BLACKJACK {LACK}{J} in {BACK}
12 Expert checking teen's latest skin condition (4) ACNE {AC{teeN}E}
14 Unknown tramp in base beginning to eat mushroom (7) EXPLODE {X}{PLOD} in {E}{Eat}
19 Holy place in Muscat renovated around end of Ramadan (7) SANCTUM {MUSCAT}* over {r...aN}
21 Mongrel beginning to bite, getting muzzle (4) CURB {CUR}{Bite}
22 Guests on island primarily getting loose motion (10) SUGGESTION {GUESTS+ON+I+Ge...g}*
25 Researcher analysed onset of cancer in testis (9) SCIENTIST {Ca...r+IN+TESTIS}*
27 Raged at elderly doc outside hospital in a callous manner (4-9) COLD-HEARTEDLY {AT+ELDERLY+DOC}* over {H}
DOWN
2 Fancy place has new, special camera accessory (4,3) LENS CAP {PLACE}* over {N}S}
3 Complete details of a nudist streaking at opening on ground (3,3,4) INS AND OUTS {A+NUDIST+St...g+ON}*
4 Oily secretion from small whitehead essentially on butt (5) SEBUM {S}{w..tEh..d}{BUM}
5 Disappears from scene, vigorously cutting guard in retreat (9) EVANESCES {SCENE}* in {SAVE<=}
8 Turns head to stare as masseur kisses amorously (11) RUBBERNECKS {RUBBER}{NECKS}
10 Urge to steal opal, take money in jars (11) KLEPTOMANIA {OPAL+TAKE+M+IN}*
15 Old cryptic clue is very elegant (9) EXCLUSIVE {EX}{CLUE+IS+V}*
18 Colonnade in dock essentially built by company (7) PORTICO {PORT}{buIlt}{CO}
20 Minor in contest, having endless energy (7) T?I?I?L (Addendum - TRIVIAL {TRI{VIm}AL} - see comments)
23 Reptile in bog at Oregon (5) GATOR [T]
24 Set up banquet in American city (4) ENID <=
Reference List
American = A, Japan = J, Unknown = X, Base = E, Old = O, Jerk = TIC, Island = I, Associate = A, Hospital = H, New = N, Special = S, Money = M
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