AAR
Refueling in the Tornado is auto-sequenced, but monitoring is important (only indicators are in the front cockpit) in case a tank fails to fill - though on the two occasions I had this it's obvious from the control feel.
Altitude/load is a bigger problem - trying to stay in contact using both burners is:
a) not allowed in the Aircrew Manual
b) f#cking difficult, for those of us who forgot that bit of the Aircrew Manual - mea culpa, those test pilots aren't wrong.
The hardest thing about AAR is when there are another 3 guys short on gas waiting their turn on your drogue, at night (or 8 guys in daytime; no pressure!!)
p.s. AAR is easier than guns tracking in ACT - that's "stuffing wet spaghetti up a wildcat's arse"