I didn't really have that much issues with free weekenders in theory but practically they were either such cluster****s or ignorants that it just amused you. Those few cases you ran into some that had some sense in their heads, it was actually quite decent.
Few interesting cases I saw:
Wave starts, the guy (can't remember the perk exactly) goes hurr durr against a mob of enemies and he dies in an instant, then followed by "ffs noobs help me". After he respawned and the new wave began, he proceeded to do the same thing again, followed by "OMFG U ****ING NOOOOBSS! HELP ME ****ERS!" and the next wave, after buying LAW (everyone else was pretty high on money at that point) and firing it once he killed himself and was like "****ING NOOB GAME U CANT FIRE A ROCKET?!?!?!?" and complained how L4D melee bash is a good feature and how ****ty KF is.
Another interesting case was that I joined a server, spawned lvl5 medic, then everyone else (lvl0-1 guys) were begging for money and said "ur lvl5 u must have money!" even though I just joined the game, followed later about how elitistic noob game KF is when high levels won't give you money to buy new top weapons... even when they just joined the game
Probably some of the more expected ones were like calling flesh pound a tank (saw this many times), bloat a boomer (many times aswell), then crawlers as hunters (lolwut?), siren as a witch (I have to admit, I did this few times when I bought the game, partitially by accident) and so on. Amusement followed when someone asked does the bloat bile attract enemies to you.
I did ran into some free weekenders who actually asked legit questions and were willing to stick around rather than proceed to hurr durr rushrush routine and die in two seconds. It was quite interesting to play with them though, a fresh change in the sea of ****e known as free weekend.