Cartoon physics, though.
The physics part isn't that bad. The sticky spiderweb keeps most of the fragments together rather than causing a huge mess of broken glass.
As for why do that to a window that was unlocked? [fantheory] Maybe Spiderman was framing a robbery as part of a insurance scam? [/fantheory]
Kissing while wearing heavy armour sure seems awkward:
"Maybe if you bend a bit more to-*CLANG* Oh dang, now were stuck."