Believe it or not there's A LOT of stuff that is up to the discretion of the cop as to whether to write you a ticket or not ... With the exception of an actual moving violation (which is cut and dry ... if you're speeding, that's a ticket ... run a redlight or stop sign, that's a ticket) anything that's subjective (exhaust noise level, underglow kits, plate visibility, the condition of your helmet) is purely at the cops discretion as far as what to do ... and as bad as it sounds he CAN write you a ticket for anything he believes is illegal, and it's up to you to take care of it after that ... once he hands you the ticket, his job is done there ... =\ sad and stupid at times, but true ...
Just some everyday examples that i'll probably get flamed for and that'll be picked apart a million times over:
If you've ever dropped your helmet it's no longer to be used on the street ... so basically if you got a serious douche pickle of a cop he could take a look at your helmet and say your helmet wasn't legal for road use if, IN HIS JUDGEMENT, it had some serious scratches on it that he deemed made it unsafe or structurally unsound ...
If, IN HIS JUDGEMENT, he thinks your plate is not visible enough ... ticket ...
Underglow kits? ... believe it or not those are illegal around here in louisiana and I've been pulled over for them before ... they were, IN HIS JUDGEMENT, deemed "distracting" by the cop, so I just turned them off and he let me go ... I've rode by other cops around here that didn't even bat an eyelash ...
If your exhaust is over a certain noise level in certain states that's illegal ... some states require measurements to be taken from about 20" away from the exhaust, others leave it up to the cops perspective (as in, if you drive by and the cop thinks your exhaust is over the limit ... he can write you and you have to go get a measurement of your exhausts noise output to see if it's over the limit or not to get the ticket dismissed) ... it's anywhere between around 85 - 95 decibels depending on the state you're in (that's an estimation from a few laws I've seen ... let's not get crazy over specifics) ... Louisiana has no set noise limits, but they can still pull you over if your exhaust is just stupid loud and write you a ticket for "modified exhaust" or something of that nature ...
Believe it or not it's illegal to ride your bike with any kind of costume on ... Got pulled over on halloween last year because my bike "matched the description of someone reported to be doing wheelies down main street" and was told that by the cop that pulled me over (he was a MAJOR douche the entire almost half an hour he had me pulled over checking everything) that, IN HIS JUDGEMENT, the costume was distracting to other drivers and that affected road safety ... he didn't write me though ...
These are just a few obscure examples of things that cops CAN pull you over for and write you for if, IN THEIR JUDGEMENT, it affects the safety of you or anyone else on the road ... and don't kid yourself, if a cop writes you a ticket whether it's justified or not it's yours to fix or pay afterwards ... I've had quite a few very questionable tickets wrote by cops in the few years I've been driving and the majority of them were dismissed but a few I still had to pay and they just agreed to keep them off of my driving record... Most of the time, they just want your moneys ... Lol