For me it has to be the abrupt rude way they first then continue to message you.there is no other group type of peope that are as commonly like thia , it doesnt matter what type of person you are everyone first message people on sites like this in the same way so being a bottom is no excuse to be rude especially considering they are after something off another person.
I often make my best effort to get to know the bottom leading up to meeting them as it gives me ideas of what gets their interest or fettish which will be used physically and verbally during play.
Anyhow should we class these people as bottoms? there are also subs,slaves,pups and pigs, i tend to class them as chasers as all the others have a certain skill mostly within relationships chasers however do just that seemingly with a haste that means they often dont bother to read profiles correctly or consider a tops may want to ask questions ie why do you want the thing you are chasing me for? or show an intrest in the person they are about to meet and of all thesites im on non of them say im a top in the profiles yet only chasers miss this and rudely message in a demanding way because they are focused on something else they have read and they to have it.
So chasers consider taking abit more carefull time in your profile searches and consider that the top may show an interest in you, andjust because the top has the thing you want doesnt make it yours to claim and the person you are seeking it of may have a particular type of person he is interested in giving it to.