FLC ON B737-300 DEPARTING LGA RWY 31 GIVEN EXPEDITE TKOF; AFTER PREVIOUS 2 ACFT HAD TKOF CANCELED. ON BECOMING AIRBORNE AT THE FAR END; THE CREW SAW A DASH-8 AT APPROX 100 FT LNDG ON RWY 22. PIC CONCERNED AND QUESTIONS WHETHER STANDARD SEPARATION EXISTED.

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3 AIRPLANES IN A ROW FOR DEP; ACR Z; ACR A AND ACR X (MY AIRPLANE) DEPARTING LGA RWY 31. ACR Z WAS GIVEN TKOF CLRNC; STARTED ROLLING AND HAD TKOF CLRNC CANCELED DUE TO CONFLICT WITH LNDG TFC LNDG RWY 22. ACR A WAS THEN GIVEN TKOF CLRNC ONLY TO HAVE IT CANCELED FOR REASONS UNKNOWN. ACR X WAS THEN GIVEN CLRNC. WE WERE ALREADY SPOOLED; RELEASED BRAKES IMMEDIATELY AND THE CTLR TOLD US WORDS TO THE EFFECT 'EXPEDITE TKOF.' AS WE CLRED THE RWY 31/22 INTXN WE SAW A DASH 8; ACR Y; AT APPROX 100 FT ON FINAL FOR RWY 22. WHILE IT WAS NOT A NEAR MISS; IT WAS LESS THAN COMFORTABLE. I QUESTION IF STANDARD SEPARATION WAS MAINTAINED AS WE WERE GIVEN TKOF CLRNC EVEN BEFORE THE PREVIOUS LNDG TFC HAD CLRED THE RWY 31/22 INTXN. IN VIEW OF THE 2 PREVIOUS MODERATE SPD 'TKOF CLRNC CANCELED' EVENTS I HAVE BEEN INVOLVED IN AND THE ACFT/ACFT VERY NEAR MISS; LGA TWR CONTINUES TO DO BUSINESS IN THEIR VERY CAVALIER; 'NO PROBS HERE' USUAL METHOD OF DOING BUSINESS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE DASH-8 LNDG ON RWY 22 WAS STILL OVER THE WATER WHEN HIS FLT CROSSED RWY 22 ON RWY 31. HE BELIEVES CTLRS AT LGA ARE CAVALIER IN THEIR HANDLING OF TFC AND AT TIMES ARE RUNNING ACFT TOO TIGHT AT THE INTXNS. ALSO SAID CTLR USED SOME PHRASE HE HAD NOT HEARD BEFORE TO INDICATE HE WANTED TO THE CREW TO EXPEDITE TKOF.