The first time it was because of an accident, they ran into each other while heading to their designated place...

The second time, the both of them obviously ignored each other. But honestly I think it's because Sehun was a bit too bouncy...

The third time, Taeyeon was already putting her arm down. But as soon as she spun around to look at Sehun, she purposely patted his head...

front view:

back view:

The fourth time...well...TAEYEON WOULD YOU QUIT GIVING SEHUN STARES?!!! lol. 

what message is she trying to convey to fangirls? "well fangirls, this boy is m.i.n.e."