Model airplane building is supposed to be a fun way to relax, but there's always at least one or two tasks involved that you just hate to do.
For me it's hinges. It's tedious, boring, and I suck at them so they always look like crap. As I rebuild the tail section of the Chipmunk, I get to do six more of these miserable little things. What a joy!
If I had to pick a second one, I'd say bending LG wire. Usually 7-8 tries results in something usable.
Clear canopy fillets and wrapping lead outs...ugh!