I too have had riders come on to the freeway, and make their way quickly over and veer into splitting without so much as a glance to check that their were no bikes coming.
Check the gap folks!
And, yeah it is irritating when bikes start splitting all over the place. This can happen from some dumbass splitting and not watching his six, causing other riders to have to find their way around his/her selfish ass.
But, I have seen many groups riding together and doing this through all lanes, which is just beyond stupid imo. Hate to say this as I usually don't pick on Harleys, but for some reason it seems to usually be loudass Harleys I see doing this. With all the noise and revving, it pisses people off, makes them drive like they have lost their minds, and generally causes an general ruckus.
I saw this many times going west up to the Caldecott Tunnel while caging. People see some loud revver coming up on the left, so they try to move right a bit, only to squeeze some dipshit in a skull face mask coming on the right, who then proceeds to get mad and gesticulate and be macho and rev his shit like crazy and kick their car and whatnot.
I always think to myself "well, you are dumb motherfucker."