EWL
It's "an" F-27 or "an" F-28 because the other alternative is too hard to say. Besides, the letter "F" is pronounced as if it begins with a vowel so therein lies the justification. Same reason we don't say "a RAAF aircraft" but rather "an RAAF aircraft" (I do anyway). But then your question was rhetorical anyway wasn't it? Note that some like to use F-27 or F-28 with an hyphen!
On the subject of late pax, there is always "The Old Check-in Late with the Excess Baggage Trick". Rarely worked in my experience though! Further on the subject of late pax, it wasn't your good self who coined the "Sorry ocker the Fokker's chocker" line was it? Such a classic line deserves to be enshrined in aviation folklore with appropriate attribution.
Cheers