Think broadly, people. Piping out "that's a load of BS" requires no effort. Let's try and have some useful discussion once in a while. Tiresome doesn't only refer to physical fatigue. That being said, though, negotiating traffic in a vehicle with a manual transmission is, without a doubt, a more active process than in an auto-equipped car. Depending on how well traffic's moving, you could be going back and forth between neutral and first gear, clutch in and clutch out repeatedly. It won't be tiring physically (no foot-operated clutch should be), but it's definitely tedious and gets old quickly. On a motorcycle with a stiff clutch it's much worse, though (especially if the weather's cold -- frozen fingers + frozen lever...terrible). Relative to that any foot-operated clutch is a piece of cake in bumper-to-bumper traffic (but still tedious in traffic). 3 Pedals + 1 hand to operate in MT vs 2 pedals and 0 hands to operate in AT. At times it definitely seems like a waste of time doing all of that moving about inside the car (clutch disengaged, first gear selected, brake out, clutch engaged (maybe light throttle), five feet forward, clutch disengaged, brake, select neutral, clutch engaged) just to move 5 feet forward in traffic every 20 seconds...compared to an AT -- release brake (maybe gentle throttle), reapply brake.
The point was simply that, relative to an automatic transmission, the manual transmission is obviously more work in traffic. There's no denying that. The disagreement that keeps coming up but never being resolved whenever this "manual's tiring" vs "No it's not. You're lame." debate comes up is really regarding whether or not the MT is significantly more work, significantly more tedious or significantly more tiring than the AT, key word being significantly. Such judgements are relative to personal experience and, therefore, entirely subjective.