You and I getting into bed upset nerd (5)
I believe the answer is:
dweeb
'nerd' is the definition.
(I've seen this before)
'you and i getting into bed upset' is the wordplay.
'you and i' becomes 'we' (we means you and I).
'getting into' means one lot of letters goes inside another.
'upset' says the letters should be written backwards.
'bed' in reverse letter order is 'deb'.
'we' inserted into 'deb' is 'DWEEB'.
(Other definitions for dweeb that I've seen before include "misfit" , "(US) idiot" , "silly American" , "anorak" , "Geek" .)