Thai food is what the guys eat on Monday nights.
Howard has to take care that the food doesn't contain peanuts due to his peanut allergy. Leonard states that every Thai restaurant in towns knows this and welcomes him with "ah, no peanuts boy" (1x16: "The Peanut Reaction").
Sheldon points out, that they eat Thai food with forks not with chop sticks (1x02: "The Big Bran Hypothesis") and other trivia.
In the end of the episode "The Monopolar Expedition" the guys eat rehydrated Thai food when living at the magnetic North Pole.
In "The Veracity Elasticity", Sheldon wants to get some Thai food near Amy's apartment and to check on the plumbing repairs. Amy doesn't want to because she lied to him.
- Despite Sheldon stating that he eats Thai food from Siam Palace on Mondays (2x06: "The Cooper-Nowitzki Theorem"), Leonard states he gets him Cashew Chicken from Schezuan Palace on Monday nights (2x16: "The Cushion Saturation").
- When Ramona Nowitzki unpacks the Thai food she brought for Sheldon the order of food items she unpacks and puts on the table changes in the single shots seen (2x06: "The Cooper-Nowitzki Theorem").
- Penny smells Chinese food and it turns out to be Thai.