We've had the stalking people thread and now we've got this! 

Doesn't have to be limited to buses; trains can count too. 

5213 stalked me on a regular basis when it was Purple.
Lost track of how many times it turned up, no matter what time of day it was, what direction I was heading in or which variant of the 20 I was needing. 
I noticed that once it went spare, it still liked taking me places. 

Currently, it's the ex-SR Barbie sets that Heaton have. Literally can't get away from them. It's primarily 156 465 which follows me about, but they don't seem fussy.
I'd say its getting on 8 or 9 times since the New Year and it's been on various bits of track across the region. I tend not to use Northern as much as I used to, but when I do, it tends to be a Barbie. It even broke down on me at the end of February! 

There's been others, but non as stand out as those.