Its a toss up for the worst - Yankee stadium in the summer, the smell from the bathrooms was horrendous, the transportation to the stadium, either public or by car is a bad adventure and the was no shelter from the sun of the rain.
The other horrific staduim was Veterans in Philly. I believe in 1983 the Dub couldn't afford and assembly site in the NYC area so we had to attend the assembly in Philly. It rained the entire time and it was extremely cold for July. Many of us got sick afterwards and then we missed time from work on top of the time we took off for the assembly.